Data representing a bitmap image of 320 pixels horizontally by 480 lines vertically is stored in an SDRAM. The amount of this bitmap image data is adjusted by a data adjustment circuit so as to obtain a bitmap image of 640 pixels horizontally by 480 lines vertically. The image of a subject is sensed by an image sensing device and sensed-image data representing a subject image of 640 pixels horizontally by 480 lines vertically is obtained. The bitmap image data whose amount of data has been adjusted and the sensed-image data are applied to an on-screen processing circuit, which proceeds to execute on-screen processing so as to superimpose the bitmap image on the sensed image. The image that is the result of superimposing the bitmap image on the sensed image is displayed on a display device. In another aspect, the image of a subject is sensed using an image sensing device, whereby YC data is obtained. The YC data is recorded on an SDRAM. The YC data is then read from the SDRAM and converted to bitmap image data in a table RAM. The bitmap image data obtained by the conversion is recorded on the SDRAM. Thus the image of a subject obtained by imaging can be converted to data representing a bitmap image superimposed on the image of the subject.