An image compression circuit 1 of the invention includes an image calculator 11, a compression-system decision unit 12, and a compression processor 13. Compression-system decision unit 12 determines a variation of pieces of image data of four adjacent pixels based on a variation in luminance Y of the pixels or variations in luminance Y and saturation S of the pixels, compresses the image data into image data of one or two pixels (RGB 888 and RGB 787) expressed by an RGB color space having a small quantization error in the case of the small variation of the pieces of image data, and compresses the image data into data including the luminances of the four adjacent pixels and pieces of image data of two pixels (YCbCr 422) expressed by a YCbCr color space having a large quantization error in the case of the large variation of the pieces of image data.