Semiconductor integrated circuit device, electronic apparatus including the same, and method of reducing power consumption

A semiconductor integrated circuit device of the present invention, which employs a supply voltage supplied from a power supply as a power source and operates in synchronization with an input external clock signal, includes detection means for detecting reduction in at least one of the frequency of the clock signal and the supply voltage and internal voltage reduction means for reducing the internal voltage of the semiconductor integrated circuit device when the detection means detects reduction in at least one of the frequency of the clock signal and the supply voltage.