An optical probe includes a probe cover, within which is installed an optical system having an illuminating optical system and a receiving optical system. An emitting region and an incidence region through which light passes are provided to a bottom surface of the probe cover, the bottom surface forming an opposing region opposite a work piece. The bottom surface forms a surface where, of the light reflected from the work piece, light following a direct reflection direction is reflected in a direction moving away from the incidence region, from a position where light emitted from the emitting region is emitted at the work piece. Accordingly, an amount of second order reflected light striking the incidence region can be suppressed and, therefore, an occurrence of an erroneous value in received light distribution can be suppressed.