A scanning circuit has path switches connected between a plurality of data flip-flop circuits of the scanning circuit for sequentially reading an output signal in synchronism with a clock. A plurality of control signal lines select the path switches to arbitrarily skip reading of the flip-flop circuits that do not require the scanning circuit and always fix a potential of the skipped data flip-flop circuit. Only the arbitrary data is read, and in the case where unnecessary data exists, reading is skipped, to thereby increase the read rate.