The controlling circuit includes power supply control circuit, oscillator, clock generator, reserve circuit and multitask enable module. When an electric device enters into electricity saving mode, oscillation clock signal generated by oscillator is stopped, and operation clock signal generated by clock generator is stopped. Digital clock signal generated by oscillation clock signal and operation clock signal is also stopped. Flash read only memory in electric device is shut down in passing by using power supply control circuit, oscillator, clock generator, or multitask enable module.