A processing device includes a processing circuit configurable according to a type of an endoscope, and a control circuit configured to detect a connection state of the endoscope, and measure a disconnection time from disconnection to reconnection. The control circuit is also configured to determine that currently and previously connected endoscopes are of the same type when the disconnection time is shorter than a predetermined time, reconfigure the processing circuit according to the type of the endoscope when it is determined that the currently and previously connected endoscopes are not of the same type, and not reconfigure the processing circuit when it is determined that the currently and previously connected endoscopes are of the same type.