PURPOSE: To check easily the fault of an entire chip by checking whether or not the control signal obtained by decoding the field of a microinstruction is supplied correctly into the chip to be controlled.

CONSTITUTION: A microinstruction is read out to a register 3 and a control field is decoded. Then a control signal is sent to a chip 5 to be controlled. The data supplied from an input data register 7 is calculated, and the result of this operation is outputted to a register 8. In such a case, the monitor bit M of the microinstruction is read out of the register 3 and sent to an exclusive AND circuit 9. While a control signal (a) supplied to the chip 5 is sent again in the form of a control signal (a') as long as the chip 5 is normal and supplied to the circuit 9. When the dissidence is detected between both signals by the circuit 9, a monitor latch 10 is set to know the fault of the chip 5.