A signal generating circuit for a real time clock device is disclosed, having an oscillating circuit, a voltage detecting circuit, and a control circuit. The oscillating circuit is used for generating oscillating signals. The voltage detecting circuit is used for detecting a voltage level coupled with the signal generating circuit. The control circuit is coupled with the oscillating circuit and the voltage detecting circuit. When the voltage level detected by the voltage detecting circuit locates in a predetermined range, the control circuit configures the oscillating circuit to generate the oscillating signals with a larger current at a first interval and to generate the oscillating signals with a smaller current at a second interval. The control circuit further generates a clock signal according to the oscillating signals at a third interval.