To reduce the level difference of light quantity received by an autofocusing sensor by constituting the branching surface of a branching optical element of plural parts and making the light transmissivity or the like of the plural respective parts different in accordance with an angle that object luminous flux made incident on a photodetecting means is made incident on the plural respective parts.

An autofocusing sensor module 7 is arranged under a porro- prism 6, a prism 22 is brought into close contact with a 2nd reflection surface 21b of the prism 6 and a boundary surface is set as a branching coating surface 11 to form a branching optical element. The luminous flux made incident on the prism 6 is branched to reflected light and transmitted light by the surface 11 and the reflected light is made incident on a focusing screen 5 and the transmitted light is made incident on the module 7 to form an image on a CCD sensor 15, respectively. In such a case, the surface 11 of a dielectric multilayer film is divided into two kinds of left and right optical branching coats 16 and 17 with the center as a boundary and the setting of the incident angles of the coats 16 and 17 are made to fit to left and right luminous flux incident angles γand α.