To provide an oriented polymer film the thermal conductivity of which has special anisotropy.

In the oriented polymer film, out of refractive indices in the longitudinal direction and in the width direction, a larger refractive index is n1, and the smaller index is n2, while thermal diffusivity in the direction of n1 is t1 (cm2/s), and thermal diffusivity in the direction of n2 is t2 (cm2/s). In the oriented film, the value of (t1/t2)/(n1/n2) is 2 or larger.