An interface circuit which outputs a clock signal and data to a data register that serially reads in the data synchronously with the clock signal, in response to a control signal changing from one level to the other level, for outputting the clock signal and the data. The interface circuit comprises a clock output circuit that, responding to the level of the clock signal when the control signal changes from the one level to the other level, outputs clocks of the clock signal that are the same in number as bits of the data to the data register.