PURPOSE: To reduce the burden of software of a microprocessor, by determining precedence with hardware in the external of the microprocessor to be interrupted.

CONSTITUTION: An encoder circuit 8 discriminates the interruption of the highest priority of output lines P1"WP8" and outputs a 3-bit code signal 9 corresponding to this interruption and an intrruption request signal INT to a buffer circuit 10 and a microprocessor 1 respectively. When detecting the interruption request signal INT, the microprocessor 1 and its peripheral parts jump to each interruption program and set a bit in a reset port 4 through a data bus 3. Then, an interruption signal of a latch circuit 6 is reset to make it possible to accept the interruption again. The microprocessor 1 sets a mask port 5 in accordance with an executing program, thereby supplying only a non-masked interruption signal to the encoder circuit 8 through a gate circuit 7.