To exactly position a welding machine moving along a track passing each welding spot of a workpiece at each welding spot without adopting expensive means such as the drive and control of a servomotor.

In a welding apparatus, the welding machine 30 moving along the track passing a plurality of the welding spots of the workpiece is positioned in each welding spot and driven/controlled for welding. A movable base 20 incorporating the welding machine 30 is moved under the gravity of a weight by being guided by a rail 14 placed along the track. A lock member 16 is fixed to a position corresponding to each welding spot of the workpiece along the rial. By engaging a lock pin 44 with the lock member 16 by driving/controlling an actuator 40 incorporated with the movable base 20, the movement of the movable base 20 is stopped. In this way, the welding machine 30 is positioned in each welding spot of the workpiece.