PURPOSE: To make it possible to detect failure of Q-switch operation by adding a detector to detect laser beams leaked from a total reflection mirror and a means to issue an alarm to the outside of the total reflection mirror.

CONSTITUTION: Optical attenuator 26 is placed behind a total reflection mirror 11, and when there is leakage from the total reflection mirror 11 it attenuates it and inputs a signal to a gate circuit 24 through a detector 21. On the other hand, a timing circuit 18 receives a signal from a Q-switch driver 15 and inputs a comparator detection inhibition signal (b) into the gate circuit 24 and the comparator 20. This comparator 20 rings an alarm buzzer 17 by an output signal (e) and stops an excitation lamp power source 16 through an alarm circuit 19 only when a signal above level E set by a level adjuster 23 is input. Hereby, processing failure by the Q-switch operation failure is prevented.