To prevent a danger caused by laser light leakage by providing a guide light source (a pilot light source) besides a laser light source, confirming which laser light outgoing side optical transmission line is connected thereto with an optical switch by the light from the guide light source before lighting the laser light source, and preventing the lighting of a laser light source when an intended outgoing side optical transmission line is unconnected.

This medical laser apparatus is provided with the laser light source 1, the guide light source 7, a light source side optical transmission line 2 transmitting the laser light and the guide light, an optical switch 3 switching the optical path of the light radiated from the light source side optical transmission line 2, outgoing side optical transmission lines 41 and 42 transmitting the lights switched by the optical switch 3 respectively, and optical sensors 81 and 82 provided in the outgoing side optical transmission lines respectively and detecting the guide light under the transmission in the outgoing side optical transmission lines. This medical apparatus is so formed as to light the laser light source 1 only when the guide light source 7 is lit and the optical sensor in the outgoing side optical transmission line selected by the optical switch 3 detects the guide light.