To reduce the deterioration of image quality by suppressing block distortion, when JPEG-compressing image data.

A high-frequency component attenuation means 15 of a cellular telephone 1 attenuates high-frequency components of the image data S0 obtained by imaging an object with an imaging means 10 at an attenuation rate α, and allows an attenuation rate storage means 30 to store the attenuation rate α. A compression means 20 applies JPEG-compression to image data S'0 obtained by attenuating the high-frequency components to obtain compressed image data D0, and the data D0 are stored by an image storage means 40. When displaying the data D0 stored by the means 40, a decompression means 50 of the telephone 1 performs expansion processing for the data D0 stored in the means 40 to obtain expanded image data D1. A high-frequency component amplifying means 55 reads the attenuation rate α from the means 30, amplifies the high-frequency components of the data D1 at the attenuation rate α, and allows a display means 60 to display the data D1.