An optical device in which a polymerizable liquid crystal material various optical characteristics of which is stable even against heating during manufacture of an optical apparatus such as an image display is cured. The optical device has a support and an optical functional layer made of a cured polymerizable liquid crystal material having a predetermined liquid crystal regularity and provided on the support. The optical device is characterized in that the optical device is subjected to a heat treatment at a predetermined temperature and in that the thickness decrease of the optical functional layer defined by (A-B)/A is 5% or less where A is the thickness of the optical functional layer after the heat treatment, and B is the thickness of the optical functional layer after the optical device is heated for 60 minutes at the heat-treatment temperature.