An optical sensor apparatus includes a light receiving element configured to produce an output according to a light receiving state, and an optical element including a reflecting layer including a metal film, and being arranged such that at least some of incident light on the light receiving element is light that is reflected by the reflecting layer. The optical element further includes a corrosion resistant layer for suppressing corrosion of the reflecting layer, and the reflecting layer includes a surface covered by the corrosion resistant layer formed by vapor plating.