PURPOSE: To omit the processing carried out by a CPU and at the same to realize the perform the complicated processing via a keyboard controller like the CPU, by defining the keyboard controller as a bus master and carrying out the hardware switching operations including a display switching operation, etc., via the keyboard controller.

CONSTITUTION: A keyboard controller 14 detects a specific key operation and gives a bus using request to a bus arbitrating circuit 19 to acquire the using right of a system bus 100. Then the controller 14 gives an access to a display interface 16, for example, based on the incorporated firmware and performs the display switching operation in response to a detected specific key operation. Hereafter the controller 14 finishes the desired processing and switches the bus using requests to open a bus to a CPU 11. Thus it is possible to carry out the accurate hardware switching operations including a display switching operation, etc., and to perform the accesses to the interface 16 via the controller 14 up to a level equal to the CPU 11.