A spatial light modulator (SLM) 101 has a multiplicity of pixels 101a arranged in a lattice form for selecting a transmission state (on) and a blocking state (off) of light on each pixel thereby spatially modulating light intensity. The spatial light modulator 101 has a light transmissivity distribution over whole pixels is set such that a light transmissivity is lower at and around a center and increased with increasing distance from the center.