Spectral characteristics are controlled with high accuracy using a variable-spectrum device provided at the tip of a long insertion portion of an endoscope, thereby acquiring a sharp observation image. An endoscope system, at least a portion of which is to be inserted into the body cavity of a living organism and which acquires an image of an observation target in the body cavity, includes, at a leading end of the portion inserted into the body cavity, a variable-spectrum device whose spectral characteristics are changed by changing a gap between two facing optical elements that are separated by the gap an actuator that changes the gap between the two optical elements in accordance with an input driving signal a sensor that detects the gap between the two optical elements and an electrical circuit to which the output of the sensor is input, which includes an active device, and which outputs an electrical signal corresponding to the output of the sensor.
