Patent ID: 8102106

Claim:
A spark plug comprising: a rod-shaped center electrode; an insulator which holds the outer circumference of the center electrode; a metallic shell which holds the outer circumference of the insulator; and a ground electrode joined to the metallic shell and forming a spark gap between the ground electrode and the center electrode, the ground electrode having a projecting portion which is formed through half punching performed by use of a working pin and which faces the center electrode, and a press-formed recess portion formed on a back surface of the projecting portion as a result of formation of the projecting portion through the half punching, wherein the press-formed recess portion is comprised of a first portion with which the working pin has come into contact, and a second portion with which the working pin has not come into contact; and a relation B 1 /B 2 ≧0.05 is satisfied, where B 1 represents a depth of the second portion, and B 2 represents a depth of the press-formed recess portion.