A micro-controller includes a dictionary memory for storing instruction codes which appear in a program, and a compressed code memory for storing compressed codes each converted from each of the instruction codes included in the program. Each compressed code has a word length sufficiently long to identify all instruction codes included in the program. Each compressed code has a value indicative of an address in the dictionary memory at which an associated instruction code is stored. The micro-controller is responsive to an instruction code read request which specifies an address of a compressed code to read the compressed code stored in the specified address in the compressed code memory, and to subsequently read an instruction code stored in an address indicated by the compressed code in the dictionary memory.