A flip-flop circuit operates by a first clock signal whose amplitude is smaller than that of input data D. A pair of transistors receive the input data D and the reversed input data *D, respectively, to latch the input data D. An activation circuit activates the pair of transistors in a conduction state. A control circuit receives the first clock signal and sets the activation circuit to a conduction state for a predetermined time period starting from an edge timing of the received first clock signal. The control circuit increases the amplitude of the first clock signal and sets the activation circuit in a conduction state by using a second clock signal which is the first clock signal with the increased amplitude.