Specularly reflected light from a convergence position on an object surface 31 enters a second critical-angle prism 14, another prism 15, and a first critical-angle prism 13 of a parallel beam selection optical system 20 in this order as a parallel beam traveling along the optical axis. The critical-angle prisms 13, 14 have critical angles of 45 degrees with respect to the wavelength of the light beam. Light beams other than the parallel light beam are removed at oblique surfaces 13a, 14a of the critical-angle prisms 13, 14, thereby allowing only the parallel light beam to exit as a regular light beam. This parallel beam is formed into a convergent light by a collimator lens 12, reflected by a half prism 11 and converged on an image pickup surface of an image pickup device 52. In this way, unnecessary noise light can be removed without placing a pin hole plate such as that placed before the image pickup plane in a confocal microscope.