PURPOSE: To shorten a refreshing wait time by performing refreshing operation successively plural times as predetermined.

CONSTITUTION: When an execution signal is impressed from a successive refreshing control signal 3, a refreshing monitor register 11 outputs an internal refreshing signal 12. Then, a refreshing operation instruction 9 is outputted from a refreshing execution control register 8 to refresh after a refreshing operation wait time is elapsed. When the refreshing operation is completed, a control part 3 outputs a refreshing address carry-up signal 4 and the register 8 outputs the next instruction to perform successive refreshing operation; when the refreshing operation is performed as many time as predetermined, i.e. four times, the signal 12 is reset. Therefore, the refreshing operation is carried out plural times in only a wait time for signal operation and the refreshing wait time is shortened substantially.