PORTABLE INFORMATION PROCESSOR

PURPOSE:To suppress the power consumption of an essential part while maintaining system performance by providing this portable information processor with a clock multiple generation part, a voltage deciding means and a clock switching part. CONSTITUTION:When power is supplied to a power supply input part 10, power is supplied from the input part 10 to a system body circuit 11 and the supplied power supply voltage is outputted to the voltage deciding part 13. The deciding part 13 decides the voltage level of the supplied voltage and outputs a decision result such as a high or low voltage to the clock switching part 12. The switching part 12 inputs a rapid (high frequency) system clock and a slow (low frequency) system clock generated from the clock multiplex generation part 14, selects either one of the system clocks in accordance with the decision result outputted from the deciding part 13 and outputs the selected clock to the clock input of the circuit 11. Consequently the power consumption of the essential part can be suppressed while maintaining system performance.