PURPOSE: To work a work uniformly by irradiating laser light reflected by a concave mirror to the work, and at the same time, enabling the concave mirror to move back and forth and tilt, and thereby shaking luminous flux of the laser light at specified amplitude.

CONSTITUTION: The laser light 11 emitted from a laser oscillator is reflected successively by a reflecting mirror 12 and a convex spherical mirror 12a, and irradiates a part 2b to be sealed. At this time, the concave spherical mirror 12a is made to move back and forth and tilt, and relfected laser light is shaked at specified amplitude in radial direction of its luminous flux. Accordingly, whole direction of tube axis of the part 2b to be sealed is heated uniformly, and sealing by pincher 5, 5 is performed satisfactorily.