To provide a heavy load type welding gun capable of reducing the stress in a base portion of a connection member and mitigating the stress concentration.

The welding gun 10 comprises a bar-shaped electrode rod 13 on a gun arm 11 via a connection member 12. The connection member 12 is constituted of two components of an adapter 14 and an electrode holder 15. The adapter 14 includes a storage recess 16 for storing a base part of the electrode rod 15 and has a tapered shape having the sectional area increasing toward the gun arm 11.