The invention provides a laser hardening tool having little laser output
loss. The laser hardening tool 100 condenses the irradiated beams
LB.sub.1 from a semiconductor laser stack 120 via a condensing optical
lens 134, and creates parallel light beams LB.sub.3 via a diverging
optical lens 142. The laser beams LB.sub.4 having been bent by a first
mirror 160 travels through an optical waveguide 150 having a rectangular
cross-sectional shape. The laser beams LB.sub.5 having been condensed by
a re-condensing optical lens 170 are irradiated through a nozzle 190 to
subject a work to hardening. The number of reflections of the laser beams
LB.sub.4 in the angular optical waveguide 150 is small, and thus the loss
of laser output is reduced.