To provide a lighting optical system of a spatial optical modulator comprising an array of micromirrors whose resolution and contrast are high.

A plane light source installed obliquely to an optical axis and a telecentric optical system are installed, the plane light source and spatial optical modulator are arranged so as to satisfy shineproof relationship, and lighting is performed by imaging the plane light sources so that a main light beam is aligned with the optical axis of lighting on all the micromirrors on the spatial optical modulator installed obliquely at a specified angle to the optical axis of lighting. Consequently, the main light beam of illumination light lighting up the individual micromirrors of the spatial optical modulator is parallel and lights up the spatial optical modulator obliquely at the specified angle. Consequently, the high resolution and the high contrast excluding stray light are obtained.