Endoscope

1. An endoscope comprising:

a distal end portion provided at a distal end of an insertion portion, and including a distal end surface which faces an insertion direction of the insertion portion and an outer circumferential lateral surface which faces a circumferential direction of the insertion portion;

a front-view observation window for observing an insertion direction of the distal end portion, which is provided so as to face toward the insertion direction;

a lateral-view observation window for observing a circumferential direction of the distal end portion, which is formed along the outer circumferential lateral surface and has a lateral observation field of view;

a light-emitting member having an emission end surface for emitting light in a distal end direction of the distal end portion;

a groove portion formed on the outer circumferential lateral surface of the distal end portion so as to be longer than the emission end surface of the light-emitting member along the circumferential direction of the outer circumferential lateral surface of the distal end portion and so as to be opposed to the emission end surface of the light-emitting member, the groove portion being on a proximal end side with respect to the lateral-view observation window;

a plurality of particles arranged in the groove portion and having a size sufficiently smaller than a depth of the groove portion, the particles illuminating an observation field of view side of the lateral-view observation window by scattering light emitted from the emission end surface of the light-emitting member; and

a transparent infill filled between the plurality of particles in the groove portion, wherein

the lateral-view observation window has a lateral field view of a wide angle larger than at least three-quarters of an entire circumference along the circumferential direction of the lateral surface of the distal end portion, and

the groove portion performs lateral-view illumination over a wide range larger than the three-quarters of the entire circumference.

2. The endoscope according to claim 1 , wherein a reflection portion for reflecting light is provided on an inner surface of the groove portion which is opposed to the emission end surface of the light-emitting member.

3. The endoscope according to claim 1 , wherein the groove portion is provided in plurality on the outer circumferential lateral surface of the distal end portion.

4. The endoscope according to claim 3 , wherein a light emitted from the emission end surface of the light-emitting member is reflected by the plurality of groove portions so as to illuminate an entire circumferential direction of the outer circumferential lateral surface of the distal end portion.

5. The endoscope according to claim 1 , wherein the distal end portion is configured by a cylindrical member having a thinner diameter than the insertion portion.

6. The endoscope according to claim 5 , further comprising an objective optical system, the objective optical system including:

a rotationally symmetrical first lens for forming an image of a subject in the insertion direction, which is arranged along a central axis of the cylindrical member configuring the distal end portion; and

a second lens arranged at a position further towards an image-forming side than the first lens along an optical axis of the first lens, and bonded with a minor lens having a mirror surface for refracting light passed through the first lens to form the image of the subject in the insertion direction and for forming an image of a subject in the circumferential direction,

wherein, at an image-forming position of the objective optical system, an image pickup surface of an image pickup device is arranged.

7. The endoscope according to claim 6 , wherein the objective optical system forms the image of the subject in the insertion direction in a circular area at a center of the image pickup surface of the image pickup device and forms the image of the subject in the circumferential direction in an annular area around an outer circumference of the circular area.

8. The endoscope according to claim 7 , wherein

the objective optical system further includes, between the second lens and the image pickup device, a rear lens group formed of a plurality of lenses, and

on an outer circumferential side of the rear lens group, the lateral-view observation window, the light-emitting member and the groove portion are formed.

9. The endoscope according to claim 6 , wherein

the objective optical system further includes, between the second lens and the image pickup device, a rear lens group formed of a plurality of lenses, and

on an outer circumferential side of the rear lens group, the lateral-view observation window, the light-emitting member and the groove portion are formed.

10. The endoscope according to claim 1 , wherein the emission end surface of the light-emitting member is arranged near a center of a length in a circumferential direction in an inside of the groove portion.

11. The endoscope according to claim 1 , wherein the emission end surface of the light-emitting member is arranged near a center of a length in a circumferential direction in an inside of the groove portion.

12. The endoscope according to claim 1 , wherein the light-emitting member is made of a light guide fiber.

13. The endoscope according to claim 1 , wherein the light-emitting member is made of a light-emitting diode.