The invention provides a code compression technology that is favorable for a micro controller or other embedded system, and for compressed codes, resulting from conversion of program codes into variable length codes, and grouped program codes, address conversion information for specifying the start address of each group and compressed code type information for specifying the code length of each compressed code contained in a group are stored in a memory, and by enabling a corresponding compressed code address to be calculated from a code address output by a CPU, code compression that is favorable for a micro controller or other embedded system is realized.