PURPOSE: To provide a focus controller for a CRT display to control with high accuracy the focus that deteriorates by the change of the screen luminance in accordance with the high band component of the video signal.

CONSTITUTION: A CRT focus controller consists of a focus control circuit 3 which controls the focus by changing the focus voltage of a CRT 1, a luminance detecting circuit 4 which detects the luminance at a prescribed position of an image shown on the CRT 1, a high band component detecting circuit 5 which detects the higher one of levels of both horizontal and vertical high band components of the video signal, a voltage level arithmetic circuit 6 which calculates the optimum focus voltage level in response to the outputs of both circuits 4 and 5, and a voltage supply circuit 7 which supplies the optimum focus voltage controlled by the output of the circuit 6 to the circuit 3. In such a constitution, the focus voltage is controlled in accordance with the luminance and the high band signal component.