To provide an optical low pass filter which can change a cut-off frequency according to the change of an imaging condition.

The incident planes of light transmitting members 31 and 32 formed from an optically isotropic photoelastic material are arranged obliquely to an optical axis. The light transmitting members 31 and 32 have a direction of inclination different by 90 degrees from each other. When stress is added to the light transmitting members 31 and 32 by a stress addition actuator 37, the light transmitting members 31 and 32 begin to function as a birefringent plate. Accordingly, luminous flux from an object is separated into two pieces of luminous flux by the light transmitting member 31, an further separated each into two pieces of luminous flux by the light transmitting member 32. The optical low pass filter in which the light transmitting members 31 and 32 varies the cut-off frequency is thus formed because separation width change with the stress.