According to one embodiment, a semiconductor integrated device which stores secret data and is capable of operating in a test mode in which a scan test with respect to an internal circuit is executed, the semiconductor integrated device comprises a mode signal receiving module configured to receive a scan mode signal designating the test mode, a mask module configured to mask the secret data when the mode signal receiving module receives the scan mode signal, and an error detection module configured to detect presence or absence of error in the secret data and to store detection result in a first flip-flop.