A significant digit number encoding unit designates a predetermined number of coefficient data items generated from image data as a set. The maximum number of significant digits that have the greatest absolute value in relation to each set every cycle is obtained and information is encoded regarding the maximum number. An absolute value is extracted for the maximum number of each coefficient data item in a set; and the absolute value is encoded at a cycle different from that of the significant digit number encoding unit. A sign encoding unit encodes a positive or negative sign of each coefficient data item in a set whose absolute value is not 0 at a cycle different from that of the absolute value encoding unit.