The invention reduces unnecessary electromagnetic radiation noise associated with a step pulse of an output signal. A random number control register is a register for controlling start, standby, stop, timing or the like of output of random number data from a random number generation circuit. Random number data outputted by the random number generation circuit is stored in a rise/fall time variable data register. The data stored in the rise/fall time variable data register is replaced by random number data sequentially generated by the random number generation circuit. An output circuit is a circuit for outputting a signal from an internal circuit of a microcomputer to an external device, and the rise/fall times of the output signal from the output circuit are variably controlled in response to the random number data stored in the rise/fall time variable data register.