Birefringence of a protective film and leakage of light in a cross-Nicole arrangement of polarizing plates may be canceled, when, as a polarizing plate protective film, using an optical film having an optical compensation layer (2) showing refractive index anisotropy satisfying a relationship of nx2≈ny2>nz2, when a direction where an in-plane refractive index gives a maximum is defined as X-axis, a direction perpendicular to X-axis as Y-axis, a thickness direction as Z-axis, and when refractive indexes in each axial direction are defined as nx2, ny2, and nz2, respectively, on one side of a base material film (1) in which each of refractive index differences represented with |nx1−ny1|, |nx1−nz1| and |nz1−ny1| has values of not more than 0.0006, respectively, when a direction where a refractive index in a film plane gives a maximum is defined as X-axis, a direction perpendicular to X-axis as Y-axis, a thickness direction of the film as Z-axis, and when refractive indexes in each axial direction are defined as nx1, ny1 and nz1, respectively.