PURPOSE: To obtain semitransparent mirror for a laser which has an inexpensive secondary laser light suppressing film and an output adjusting film, by providing a multilayered interference reflecting mirror on one surface of a transparent base as a mirror surface and an absorptive film on the other surface.

CONSTITUTION: On the reverse side of a base 1, an absorptive film 22 is provided to attenuate various secondary beams T22 and T23 and T24 much more greatly than a primary beam T12 by absorption while relatively reducing the attenuation of the primary beam T12 due to absorption. Then, a film material is selected while attention to the thickness (d) and coefficient α of absorption is paid. Namely, the product αd is set to about 5×10-1 so as to obtain the intensity ratio of the secondary beam to the primary beam 1% less than that of a conventional laser semitransparent mirror having a reflection preventive film 21. Thus, an inexpensive, excellent-operability semitransparent mirror for a laser which has a secondary laser light suppressing film and an output adjusting film is obtained.