A phase comparing unit (130) compares a phase of an imaging-side synchronization signal with a phase of a display-side clock, and controls oscillation of a display-side clock generating unit (129) based on a result of the comparison. A display timing adjusting unit (122) receives a video signal output from an endoscope (101) at a timing based on the imaging-side synchronization signal and adjusts a synchronization timing of the received video signal to a synchronization timing based on a display-side synchronization signal.