A microcomputer comprises: a memory which stores a predetermined program; a CPU which reads the program stored in the memory based on a predetermined instruction to perform a predetermined calculation; and a read controller which controls reading of the program from the memory, and the microcomputer further comprises: a plurality of memory areas disposed in the memory and having distinction bits; distinction unit for distinguishing the memory areas using the different distinction bits; and read access controller for prohibiting the reading from the memory area in which another program is stored based on a distinction result of the distinction unit.