PURPOSE: To immediately start the self-refreshing operation and to increase the operating speed when self-refreshing instruction is inputted in an SDRAM operated in synchronization with a clock signal (a system clock signal) supplied from the outside.

CONSTITUTION: When self-refreshing instruction is fetched, a selfrefreshing signal SR in a first cycle is outputted in synchronization with the rising edge of the oscillation output of an oscillator circuit 25. The self-refreshing signal SR after a second cycle is outputted in synchronization with the rising edge of the frequency-divided output of a frequency divider 26.