PURPOSE: To enable independent monitoring and thereby realize reliable APC drive by eliminating mutual interference between a couple of laser beams for monitoring in a semiconductor laser device to be used as a light source of an optical disk apparatus, etc.

CONSTITUTION: A 2-beam array semiconductor laser chip 1 is mounted on a Si substrate 8, a couple of laser beams 11 emitted from the rear end face 10 of such laser chip are changed in the direction for 90° with a couple of mirror surfaces 12a, 12b of a triangular mirror 12 and the reflected laser beam 11 are directed to each photodiode formed on a Si substrate 8 at the lower part of each beam splitter 13, 14 through a couple of beam splitters 13, 14.