Input circuits connected to an external input terminal PAD via resistor elements are activated in response to the level transition of the clock signals supplied thereto for accepting input signals. In order to input signals applied to the external input terminal PAD clock signals having different phases are supplied to the respective input circuits. The cycle time of each one input circuit can be made longer by sequentially assigning the serial data supplied to the external input terminals in response to the clock signals having different clock signals. Since the input circuits are isolated from each other by means of the resistor elements, the influence of the kick back signal which occurs at first stage of each the input circuit upon the other input circuit can be made very small.