PURPOSE: To supply a phase adjustment device which can complete the adjustment of a phase within the vertical blanking period of a video signal.

CONSTITUTION: Insertion circuits 4 consist of counters which count at every horizontal period of the video signal and which are reset in a vertical period and signal addition parts adding the data signal of the counters to the horizontal blanking period of the video signal, and the circuits 4 add the data signal to the video signal and output it. Phase adjustment parts 5 separate the data signal from the video signal outputted from a switch 7 and adjust the phase of the video signal in correspondence with the data signal. Thus, the phase of the video signal can be adjusted in a horizontal period unit by the data signal added to the video signal.