Abstract: A polymeric optical low-pass filter of the birefringent type is provided which is lightweight and small, and which can be easily produced. Also provided are a polymeric optical low-pass filter device including the polymeric optical low-pass filter; and a composite optical filter including the polymeric optical low-pass filter. The optical low-pass filter comprises an optically anisotropic polymer film in which the displacement distance S between the ordinary ray and the extraordinary ray represented by the following formula is 1-70 .mu.m:S={(b.sup.2 -a.sup.2)/2c.sup.2 }.multidot.sin 2.phi.e,wherein a=1/n.sub.e, b=1/n.sub.0, c.sup.2 =a.sup.2 sin.sup.2 .phi.+b.sup.2 cos.sup.2 .phi., n.sub.e is the extraordinary-ray refractive index, n.sub.0 is the ordinary-ray refractive index, .phi. is the angle formed between the normal at the plane of incidence of light from a subject and the optic axis of the polymer film, and e is the thickness of the polymer film.