PURPOSE: To freely enlarge and reduce an image displayed on a screen crossways or lengthwise or crossways and lengthwise by changing frequency of a dot clock signal independently regardless of frequency of a horizontal synchronous signal.

CONSTITUTION: It has a video signal generation circuit to create a video signal to CRT by way of reading out a data from a frame memory 3 by an address signal which is a parallel output of a counter 2. Dot clock generation circuits 5a-5c to supply to the counter 2 and a synchronous clock generation circuit 7 to supply to a synchronous signal generation circuit 4 are separately and independently provided, and accordingly, it comes to be possible to change frequency of a dot clock independently regardless of frequency of a horizontal synchronous signal. Consequently, it is possible to optionally set frequency of the dot clock. Accordingly, it is possible to acquire a display device which can enlarge and reduce an image displayed on a screen freely crossways or lengthwise or crossways and lengthwise.