A reference voltage generating device including a reference voltage source, a charge supplying source, a first switch, a second switch, a charge storage unit and a logic unit is provided. First terminals of the first and second switches are respectively coupled to the output terminal of the reference voltage source and the charge supplying source. When a power on reset signal is received, the first switch is turned off and the second switch is turned on, such that the charge supplying source quickly charges the charge storage unit. When the output voltage is greater than or equal to the reference voltage, the first switch is turned on and the second switch is turned off, such that the reference voltage source maintains the output voltage to the reference voltage.