PURPOSE: To improve operating characteristic and eliminate mis-operations by automatically selecting EE set values complying with image plane sizes of an endoscope simply through mounting of the eyepiece part of the endoscope to an adapter.

CONSTITUTION: A changeover mechanism 21 whose operating lever 24 is elastically protruded at its end part 27 from inside surface 23 by a compression coil spring 26 is provided to the inside of an adapter 11 comprising providing a camera 12, and further a changeover switch 25 is provided to the rear end of said operating lever 24. As the eyepiece part 15 of an endoscope 14 is inserted into the adapter 11, the operating lever 24 moves to operate the changeover switch 25, by which resistances 28, 30 are changed over to control a photometry circuit 20 which in turn automatically selects the EE set value conforming to the image plane size of the endoscope 14. As a result, there is no need for the operate to change over the EE set value according to the kinds of the endoscope, thus operating characteristic may be improved and mis-operation prevented.