To prevent the peeling of a translucent reflecting film from the substrate as well as to suppress the cracking of the film due to a thermal shock and to prevent the deterioration of the function by making the coefft. of linear expansion of each of the film and a hard coating film lower than that of the substrate.

This optical half mirror 1 has a transparent substrate 2 made of a synthetic resin, a translucent reflecting film 3 formed on the substrate 2 and a hard coating film 4 coating the film 3. The coefft. of linear expansion of each of the films 3, 4 is lower than that of the substrate 2. The thermal expansion and shrinkage of the substrate 2 are suppressed by the coating film 4 and the cracking of the reflecting film 3 due to sudden thermal deformation of the substrate 2 can be prevented. Since the reflecting film 3 is coated with the coating film 4, the peeling of the film 3 from the substrate 2 is prevented even if the film 3 cracks and the function can be maintained.