To provide a polarization separation device in which the degree of parallelness between transparent substrates is highly maintained, the adhesion strength is enhanced and peeling is hardly caused.

The polarization separation device 1 has a birefringent grating layer which consists of: layers of a birefringent film 3 having a grating 8 with a periodical rugged pattern formed; and an overcoat layer 4 formed by applying an isotropic material on the grating of the periodical rugged pattern to fill the pattern and on the whole surface of the birefringent film 3 and which is interposed between transparent substrates (2, 6). The device 1 has a space 7 to be filled with an adhesive and formed by removing a part of the birefringent film 3, and the space 7 is filled with an adhesive. The thickness of the overcoat layer 7 from the face in contact with the upper face of the projections of the grating with the periodical rugged pattern of the birefringent film 3 to the face in contact with the transparent substrate 7 in the opposing side to the upper faces of the projections is ≤10 μm.