Endoscope

1. An endoscope comprising an insertion portion that includes a distal end portion, and a bending portion configured to change a direction of the distal end portion, the bending portion being provided so as to extend from the distal end portion, wherein:

the distal end portion includes a casing having a round shape in a cross-section, and an image pickup module that includes an optical module section including a plurality of optical members and an image pickup sensor, the image pickup module having a rectangular shape in a cross-section;

the image pickup module includes a semiconductor stack in which a plurality of semiconductor devices is stacked;

an entirety of the image pickup module is completely housed inside the casing;

an end of an operation wire configured to bend the bending portion is fixed in a space over a side face of the image pickup module; and

a maximum length of a cross-section of the space is no less than 100% and no more than 112.5% of an outer dimension of the fixed end;

the operation wire having a round shape in a cross-section; and

a diameter R 50 of the operation wire, a length D 30 of the image pickup module and a diameter R 40 of the casing meet the following expression:

( R 50+ D 30+ R 50)≤ R 40≤1.25×( R 50+ D 30+ R 50).

2. The endoscope according to claim 1 , wherein the end of the operation wire is fixed to the side face of the image pickup module.

3. The endoscope according to claim 1 , wherein the end of the operation wire is fixed to an inner face of the casing having a cylindrical shape.

4. The endoscope according to claim 1 , wherein:

the casing is formed of a molded resin in which the image pickup module is embedded; and

the end of the operation wire is embedded in the molded resin.

5. The endoscope according to claim 1 , wherein the image pickup module is a wafer-level stack.

6. The endoscope according to claim 1 , wherein an outer diameter of the casing is less than 1 mm.

7. The endoscope according to claim 4 , wherein an outer peripheral portion of a distal most optical member of the plurality of optical members includes a stepped portion, and molded resin covering an outer peripheral face of the optical module section is filled in the stepped portion.

8. The endoscope according to claim 1 , wherein a material of the casing is a light-shielding member.

9. The endoscope according to claim 4 , wherein the molded resin includes a light-shielding material.