The invention provides: an optical element that includes a birefringence functional layer constituted of a polymerizable liquid crystal material, in which the birefringence functional layer is formed directly or indirectly on a substrate, and in a post-process carried out thereafter, alignment and characteristics of the birefringence functional layer are not disturbed, with the result that a high quality birefringence control function can be exerted; a liquid crystal display device provided with the optical element; a method of evaluating a birefringence functional layer that is not disturbed in the alignment and physical properties by the post-process; and a method of producing the optical element. The optical element includes at least a light-transmitting substrate; and a birefringence functional layer made of a polymerizable liquid crystal material, wherein the birefringence functional layer is formed by aligning a polymerizable liquid crystal monomer having a polymerizable group at least at one terminal thereof directly or indirectly on a substrate followed by fixation, and a degree of reduction of residual double bonds in the birefringence functional layer before and after heat treatment at 250° C. for 1 hr is less than 0.25.