PURPOSE: To detect even an address fault in addition to a data fault at the time of detecting faults in a storage circuit.

CONSTITUTION: At the time of writing data in the storage circuit 1, data obtained by finding out exclusive OR between a part of writing data and the parity of the writing data by a writing data EX-OR circuit 2 and writing data which are not used for exclusive OR operation are together written in the circuit 1. At the time of reading out data from the circuit 1, exclusive OR data obtained between a part of data read out from the circuit 1 and the parity of writing data through a reading EX-OR circuit 3 and data which are not used for exclusive OR operation are together read out as reading data. The parity check of the reading data is executed by a parity checking circuit 4 to detect the presence of a fault.