To firmly suppress a work by a press roller at the laser beam irradiation position.

Flange parts 2a, 3a as lapped works are welded by the laser beam 12a while being pressed by press rollers 21, 22. The press rollers 21, 22 are separated in the width direction of the flange parts 2a, 3a, and the just intermediate position between the pressing positions is the irradiation position of the laser beam 12a. The press rollers 21, 22 are inclined, a center part 21a of the upper press roller 21 is non-rotatable while only an outer circumferential part 21b is rotatable, and a through hole 21c which the laser beam 12a passes through is formed in the non-rotatable center part 21a.