When a CPU provided with a latch memory is operated, a constant storage method or an end storage method is selected depending on what is processed by the CPU; thus, the CPU provided with a latch memory has low power consumption. When the CPU provided with a latch memory is operated, in the case where the number of times of turning on and off the power source is high, a constant storage method is employed and in the case where the number of times of turning on and off the power source is low, an end storage method is employed. Whether a constant storage method or an end storage method is selected is determined based on the threshold value set depending on power consumption.