A time required for an output voltage of a source follower to rise from Low to a predetermined voltage depends on a bias voltage. Therefore, by setting a converged voltage of an output voltage to be high by increasing the bias voltage, the time required to rise up to the predetermined voltage can be reduced. Therefore, a first source follower which is biased so that the converged value of the output voltage becomes a predetermined Hi voltage when an input data signal goes from Low to Hi, and a second source follower which is biased so as to become the Hi voltage after a period of one clock when an input data signal goes from Low to Hi, are used. The two source followers are operated with appropriate timing.