PURPOSE: To operate a dimmer function constantly and surely by transferring a signal indicating the brightness of an object without being affected by a contact resistance of an electric contact part at a connection part.

CONSTITUTION: This endoscope system has a camera 1 to take an endoscope image obtained with an endoscope 3 and a light source device 2 to supply an illumination light for observation to the endoscope 3 and the camera 1 and the light source device 2 are connected together through a connector 5 with a signal cable 4. The camera 1 is provided with aV/F converter 10 and the light source device 2 with an F/V converter 15, respectively and a signal indicating the brightness of an object from a CCU9 of the camera 1 is converted to a signal modulated in frequency or in pulse to be transferred to the light source device 2. Then, the signal is converted back to the original signal with the light source device 2 to be sent to a stop control circuit 14 to control a stop 13 thereby accomplishing a dimmer operation of the light source device.