Push switch

1. A push switch comprising:

a first fixed contact;

a second fixed contact disposed apart from the first fixed contact;

a movable contact facing the first fixed contact with a space therebetween, the movable contact being metallic and dome-shaped; and

a protrusion disposed above a center of the movable contact,

wherein when the protrusion is pressed, the movable contact elastically deforms, and while remaining deformed, the first fixed contact and the second fixed contact are electrically conductive with each other via the movable contact,

wherein the protrusion is elastic,

wherein a first force deforms the movable contact and a second force less than the first force maintains the movable contact deformed while the first contact and the second contact are electrically conductive with each other.

2. The push switch of claim 1 , further comprising:

a sheet covering the movable contact,

wherein the protrusion is formed on the sheet.

3. The push switch of claim 1 ,

wherein the protrusion is formed of elastomer.

4. The push switch of claim 1 ,

wherein a following formula is established,

40≦( P 1 −P 2)×100 /P 1≦60

where P 1 represents a pressure before the elastic deformation of the movable contact, and

P 2 represents a pressure after the elastic deformation of the movable contact.

5. The push switch of claim 1 , further comprising:

an operation button including an operation part and a pressing part, the operation button being disposed above the protrusion,

wherein when the operation part is pressed, the pressing part presses the protrusion.

6. The push switch of claim 1 ,

wherein the protrusion has hardness according to JIS K durometer type A of 55 or more.