Abstract: A first and second semiconductor memory circuits and a redundant circuit for realizing a defect relief function are made connectable, whereby the redundant circuit is shared between the two semiconductor memory circuits, and when a failure occurs in either of the semiconductor memory circuits, the redundant circuit operates as a portion in the semiconductor memory circuit. Consequently, the defect relief function can be added to each of the two semiconductor memory circuits by only adding one redundant circuit and redundant changeover switch groups.