PURPOSE: To easily recognize the rough value of remaining data capacity which is simple in a calculation constitution and is possible to be stored based on a calculated value by displaying the value by calculating the present usable data capacity from a preliminarily determined number of data, total memory capacity and the present address.

CONSTITUTION: A horizontal address counter 7 counts a horizontal clock signal when a horizontal clock count enable (/CLKE) is for an 'L' period. A vertical address counter 8 counts an I-1 synchronizing signal when an H synchronizing signal enable (/HE) is for an 'L' period. A horizontal clock counter is the sampling clock (DOTCLK) of image data. The values of numbers of frame K and k can be easily calculated by the software calculation by a CPU 14. The CPU 14 displays the values of K and k on a display part 13 via a display driver 12. By this display, a user can recognize the number of screen which can be stored in a memory 3 by both modes in the both cases of a data compression and a data non-compression.