PURPOSE: To make parameters changeable when phase difference and amplitude transmittance are approximated by stepwise distribution, and facilitate manufacturing.

CONSTITUTION: In an optical filter the following are arranged in order from the light incident side; a polarizer 31, a quarter-wave plate 32, a polarization ring belt plate 33 and analyzer 34. Light which has passed a mask passes the polarizer 31, turns to linearly polarized light, and passes the quarter-wave plate 32. Hence the phase difference between linearly polarized light components whose planes of polarization intersect perpendicularly each other becomes equal to π/2. The polarized light passes the polarization ring belt plate 33 and the analyzer 34. Between the lights which have passed two regions corresponding with a circle type polarization part 33a and a ring type polarization part 33b of the polarization ring belt plate 33, phase difference and amplitude transmittance are generating according to an angle θ1, an angle θ2, the transmission axis azimuth A of the circle type polarization part 33a and the transmission axis azimuth B of the ring type polarization part 33b. Hence parameters are changeable when the transmittance is approximated by stepwise distribution.