PURPOSE: To constitute the microcomputer so that the respective input clocks supplied to plural peripheral circuits in the microcomputer are selected and can be outputted to the outside.

CONSTITUTION: The microcomputer is provided with a clock switching switch circuit 7 for selecting the respective input clocks a, b,-k supplied to clock input terminals 51 of plural peripheral circuits 5a, 5b,-5k such as a timer, an A/D converter, a serial I/O, etc., in the microcomputer 1, and outputting them to the outside, and a clock switching control circuit 9 for controlling this clock switching switch circuit 7.