To obtain a reflecting type optical apparatus which can be more highly accurately optically registered by detecting to which point on a reflecting face of a reflecting type optical element the light is shed.

In this reflecting type optical apparatus, a light 5 is obliquely brought to a reflecting face of a reflecting type optical element 1 and the incident light 5 is reflected by the reflecting face. The reflecting type optical apparatus has a photodetector 3 arranged opposite to the reflecting face of the reflecting type optical element 1 for detecting an intensity of a secondary radiation light radiated from the reflecting face when the light 5 is obliquely incident on the reflecting face. The reflecting type optical apparatus can accordingly be optically registered simply and accurately.