A register for a scan test has a data saving function. A scan flipflop includes first to third memory circuits. The first memory circuit is a memory circuit functioning as a register of a combination circuit in normal operation. The second memory circuit is a memory circuit for backup of the first memory circuit. The third memory circuit has a function of transferring data to a flipflop in a next stage. Further, the second memory circuit has a function of writing data of the first memory circuit to the third memory circuit and a function of writing data of the third memory circuit to the first memory circuit. At a given time, data of the first memory circuit can be extracted from an external device and data can be stored in the first memory circuit from an external device.