The invention provides an optical apparatus enabling diopter adjustment, etc. to be achieved using, for instance, a reflection type variable-optical property optical element or a variable-optical property mirror but without recourse to any mechanical moving part. The variable-optical property mirror 9 comprises an aluminum-coated thin film 9a and a plurality of electrodes 9b. Via variable resistors 11 and a power source switch 13 a power source 12 is connected between the thin film 9a and the electrodes 9b, so that the resistance values of the variable resistors 11 can be controlled by an operating unit 14. The shape of the thin film 9a as a reflecting surface is controlled by changing the resistance value of each variable resistor 11 in response to a signal from the operating unit 14 in such a manner that the imaging capability of the variable mirror is optimized.