To prevent a general personal computer from affecting its real time property in a simple and inexpensive way by connecting a 2nd CPU unit to a local bus and also connecting a real time processing system unit to a general- purpose bus in a real time processing mode.

A 2nd CPU 21 is connected to a local bus 3 and stops the general-purpose operation system of a 1st CPU 1 in a real time processing mode. Thus, the CPU 21 can instantaneously cope with a real time event that is always operating. The CPU 1 is basically operating but the CPU 21 stops the CPU 1 and accesses the bus 3 when the CPU 21 obtains the bus access right. When the bus access of the CPU 21 is not needed, the CPU 21 gives the bus access right to the CPU 1. In other words, the CPU 21 cancels the stoppage of the CPU 1 and actuates the CPU 1.