PURPOSE: To enhance the throughput for a system having a memory, by varying a producing frequency of a refresh clock pulse in accordance with the change of the ambient temperature.

CONSTITUTION: The refresh interval of the dynamic RAM varies according to the ambient temperature. The cycle of the refresh clock pulse is varied ib accordance with the change of the ambinet temperature to minimize the time during which the bus line is occupied for refresh in accordance with each temperature. For instance, the oscillation frequency sent from the output terminal OUT is varied by making use of the fact that the resistance value of the thermistor Rx varies by the temperatures. In such way, the throughput is enhanced for the system having a memory.