To reduce the size of this device, to make this device light, and to lengthen the life of this device by reducing heat dissipation and power consumption.

This microelectronic device is provided with a plurality of functional units 108, 110, 112, and 114 necessary for executing a machine code instruction, a system clock 104 to be supplied to those functional units, and a logical unit 116 for controlling those functional units by monitoring the machine code instruction. The logical unit 116 monitors the machine code instruction, and preliminarily selects the cycle quantity of the system clock for discriminating the specific functional unit necessary for executing the next machine code instruction and a total cycle period since the specific function unit is put into a condition that its preparation for executing the machine code instruction is completed until the specific unit is turned off after executing the machine code instruction, and discriminates the specific function unit based on the cycle quantity, and turns on/off the specific functional unit in the total cycle period.