An electronic endoscope system has a personal computer, an adjustment monitor and an adjustment processor unit. The personal computer is for changing parameters related to image quality of an endoscopic image. The adjustment monitor displays an adjustment screen, showing information of the parameters, synthesized on an endoscopic image. The adjustment processor unit is connected to the personal computer and the adjustment monitor. The adjustment processor unit produces adjustment data in a data producing section in accordance with changes of the parameters input from the personal computer and sends the adjustment data from a transmitter to an electronic endoscope. The adjustment processor also receives an imaging signal from the electronic endoscope by a receiver and produces the endoscopic image from the imaging signal in a signal processing section. The adjustment processor then synthesizes the adjustment screen onto the endoscopic image and outputs the synthesized image to the adjustment monitor.