PURPOSE: To cope with multiple kinds of products without stopping a device by dividing a slide table into plural ones, making them slidable respectively independently, and fixing one positioning head to each of the slide tables.

CONSTITUTION: Positioning heads 7 and 8 to set positions of a frame 2 and a holder 3 are arranged on respectively independent slide tables 15 and 16, and the respective positioning heads 7 and 8 are introduced separately into a welding booth 9. Welding units 10 and 11 move to prescribed positions in the welding booth 9, and weld the positioned frame 2 and holder 3 together. After welding is finished, the positioning head 7 can move the slide table 15 to the operator side without being influenced by a condition of the other positioning head 8. Thereby, even if the positioning head 7 side is in production, the positioning head 8 side can switch the kinds of products.