A microcomputer of the present invention permits a direct control of a rewrite operation on an internal flash-memory to enhance the efficiency of a debugging operation. The microcomputer has a first storage means that stores a program for rewriting data into an internal flash memory, a second storage means that stores internal flash information about the internal flash memory, an interface that makes a connection to a debugging tool, and a CPU. The CPU allows reading of the internal flash information by the debugging tool through the interface, receiving of write data based on the internal flash information from the debugging tool through the interface, and rewriting of the write data as new contents into the internal flash memory in accordance with the program for rewriting data into the internal flash memory.