A flip-flop circuit consuming lower power than a conventional flip-flop circuit is provided. Further, a flip-flop circuit having a smaller number of transistors than a conventional flip-flop circuit to have a reduced footprint is provided. An n-channel transistor is used as a transistor which is to be turned on at a high level potential and a p-channel transistor is used as a transistor which is to be turned on at a low level potential, whereby the flip-flop circuit can operate only with a clock signal and without an inverted signal of the clock signal, and the number of transistors that operate only with a clock signal in the flip-flop circuit can be reduced.