To prevent admission of useless light into a light guide during the unuse period of an electronic endoscope.

An image signal processing circuit 26 receiving an image signal from an image sensor of an endoscope inputs the image signal into a system controller 24. A temperature sensor 28 detects the temperature at the tip of a cap 19 inserted into a socket 20a to input the result of the detection into the system controller 24 via an A/D converter 27. When the temperature at the tip of the cap 19 is above a set value while the image signal is kept unchanged over a fixed period of time, the system controller 24 controls a stop wing driver 25 to make a stop wing 36 shield the white light down to its minimum.