PURPOSE: To read and write the data from an external part to a memory cell in a conductor redundant bit array by disabling an error detecting signal by a control signal from an external part and selecting simultaneously the bit line connected to the memory cell in a redundant bit array with a selector circuit.

CONSTITUTION: When the control signal ECCSTP of an ECC function stoppage is enabled, a coding circuit 4 and an error detecting circuit 5 are not usually operated, the output B of the coding circuit 4 comes to be a high impedance condition and inspection information is not inputted to a redundant bit array. An error detecting signal ED, which is the output of the error detecting circuit 5 comes to be a disabling condition and the information in a memory cell is sent through an input/output circuit 7 to the external part as it is. On the other hand, a selector circuit 3 not only can select a bit line connected to the memory cell in the information bit array, but also can select bit lines A and A' connected to the inside of the redundant bit array. Consequently, optional data can be written and read.