In an ECC circuit of an ECC circuit-containing semiconductor memory device, an error correcting code/syndrome generating circuit and a data correcting circuit are disposed. In portions of the ECC circuit connected to buses, a data bus input control circuit for controlling input of a data from a data bus; an error correcting code bus input control circuit for controlling input of an error correcting code from an error correcting code bus; and an error correcting code bus output control circuit for controlling output of an error correcting code to the error correcting code bus are disposed. A portion corresponding to an error correcting code generator of a conventional technique is included in the ECC circuit, so that the ECC circuit can function both as an error correcting code generator and a decoder. As a result, the entire device can be made compact.