PURPOSE: To improve the condensing state to a focus, by providing a nonvisible laser beam reflecting film to the rear surface of a coupling optical member and further partially providing a visible guide beam reflecting film behind said film and guiding treatment laser beam and visible guide beam from the front surface of the coupling optical member to respectively reflecting both beams by the reflecting films.

CONSTITUTION: A operator confirms that a visible guide beam L2 is focused to emit a treatment laser beam L1 from a laser beam source 11. Since an optical membrane 16a permitting the visible guide beam L2 to transmit and reflecting only the treatment laser beam L1 is applied to the entire rear surface S2 of a mirror coupling optical member 16, the treatment laser beam L7 incident to the mirror coupling optical member 16 from the front surface S1 thereof is reflected from the rear surface S2 to be condensed to the focal position of an eye E to be treated. Further, since the optical membrane 16a receives no effect due to the thickness of optical membranes 16b, 16c, the disturbance of a wave front is not generated in the treatment laser beam L1 reflected by the optical membrane 16a. Furthermore, even the beam reflected from the rear surface generates no astigmatism and a focal position is also not shifted.