To provide a method for manufacturing optical devices by which the joint surface of two prisms can be made uniform and very small optical devices can be manufactured.

Two glass plates having a prescribed thickness, length and width are joined via an adhesive to form a plate laminate and this plate laminate is cut parallel to one lateral face in a prescribed width in such a way as to make bottom faces nearly square to form a plurality of blocks to be polished in a prescribed length, wherein joint surfaces extend parallel nearly at the centers. The four corners of each of the blocks to be polished are polished in such a way that the joint surface becomes a diagonal line of the square bottom face to form a regular quadratic prism-shaped device continuum in which optical devices range and the device continuum is cut at prescribed intervals to form a plurality of optical devices.