A compressed data generator compresses, by using a lossless compressor and a lossy compressor, image data in units of first blocks to generate a plurality of types of compressed data. A selector performs selection processing in units of second blocks each including a predetermined number N of first blocks, where N is an integer of 1 or more. The selection processing involves determining whether each of the plurality of types of compressed data satisfies a selection condition and selecting one piece of compressed data that satisfies the selection condition. The selection condition includes a data size condition that a data size of all the first blocks included in the second block is less than or equal to a predetermined value, and a data accuracy condition that information maintaining accuracy is highest among compressed data that satisfy the data size condition.