To provide a laser beam welding apparatus, wherein an optical fiber is freely shiftable.

The optical fiber 6 for guiding the laser beam is held to be freely rotatable in X-axis and Y-axis and respective rotating amounts are measured with encoders 14, 15, and a reflecting mirror 11 is rotated with motors 16 and 17 into the reverse direction to the measured rotating amount, so that the irradiating direction from the reflecting mirror 11 for laser beam always becomes constant, regardless the shifting of the optical fiber 6.