Two data processing units having the same function, one of which is used for a master and the other for comparison, are provided, control of a circuit unit is performed by the master, the master data processing unit and the circuit unit are operated in synchronization with a first clock signal, the second data processing unit is operated in synchronization with a second clock signal having the same cycle and different phase from the first clock signal, and processing results of both the data processing units are compared in a comparison circuit. Flip flops are disposed on a signal path from the circuit unit to the comparison data processing unit and on a signal path from the master data processing unit to the comparator, and both the first and second clock signals are used for latch clocks of the flip flops in accordance with input signals thereof.