PURPOSE: To reduce power consumption and to suppress internal heat generation by providing the feed line of each function block of a one-chip microcomputer with an electric power supplying and cutting function and setting this function according to the program of a mask ROM.

CONSTITUTION: A power cutting block 7 connects and disconnects the power supply line 2 of the one-chip microcomputer 1b to and from feeding lines 61W63 extending to respective function blocks 51W53. A block 7 corresponding to the program set in the mask ROM3 is set to inhibit power supply to other function blocks which are not used, and consequently the power consumption is reduced to suppress internal heat generation, improving the reliability.