PURPOSE: To enable small diameter of a supporting member and to execute laser quenching to inner peripheral face in a small diameter hole by constituting the titled working head so as to execute cooling of a bent mirror irradiating especially the inner face of hole bored in a work by using a heat pipe.

CONSTITUTION: After positioning the lower end part of the mirror supporting member 19 by inserting into the hole H in the work W, the laser beam LB is generated 5 and radiated to the bent mirror 17 from upper direction through optical system in the working head 15. Therefore, the beam LB is horizontally reflected to irradiate the inner peripheral face of the above hole H. Then, at the time of rotating inner cylindrical member 31, etc., by working a servomotor 37, the supporting member 19 is rotated around the optical axis and the beam LB is made to one round while irradiating to the inner peripheral face in the hole H. In this result, the laser quenching can be executed to the inner peripheral face in the hole H. During this operation, temp. of the mirror 17 tends to raises, but as the heat of the mirror 17 is transferred directly to the heat pipe 47 and to the heat pipe 47 through a base seat 45, the cooling of the mirror 17 can be effectively executed.