To prevent the control and the structure from being complicated and to prevent the weight from being increased.

A guide device is composed by being provided with a guide rail 11 extending in the state of curving in copying the center position Wc of the thickness in a sun roof reinforcing part W, a slider 32 holding a spot welding gun 40 and being arranged movable following to the curved shape of the guide rail 11, a slide shaft member 30 and a copying running member 20. The movement of a shifter 52 is transmitted through a cam plate 53 and a cam follower 24, these slider 32, the sliding shaft member 30 and the copying running body 20 are made to move against the guide rail 11.