To provide a welding gun capable of improving the durability by effectively bearing the load in the thrust direction, and capable of providing a heavyweight and large-sized movable gun arm, even in a small-sized main body unit. A welding gun 10 of a guide groove type is provided with a thrust direction guide mechanism including: two guide pins 19a and 19b provided to an arm holder 13 in an integrated manner by penetrating first and second guide grooves 17a and 17b; brackets 23a and 23b being fixedly provided to the end portions of the guide pins 19a and 19b, and having a length sufficient to traverse the first and second guide grooves 17a and 17b in a direction orthogonal to the axis line of the guide pins 19a and 19b; and thrust bearing members 24a and 24b being provided to the end portions of the brackets 23a and 23b, abutting on a side plate 11a of a gun body 11, so as to be movable along the first and second guide grooves 17a and 17b.