PURPOSE: To prevent reduction in a received light quantity in remote distance communication without need of a lens with a large aperture and a highly accurate major mirror.

CONSTITUTION: Optical flux emitted from an light emitting element 11 is collimated by a light projection optical system 12, reflected in a beam splitter 13 and emitted from a hollow part of a sub mirror 16 and an emission optical system 17 as a transmission beam La in the transmission. A received beam Lb from an opposite equipment is reflected in a mirror coating part applied to the circumference of a major mirror 18 and the emission optical system 17 and transmitted through a mirror coating part of the beam splitter 13 and a light receiving optical system 14 and received by a light receiving element 15 in the reception.