A constant voltage boost power supply according to an aspect of the invention includes a voltage-controlled variable frequency oscillator that produces and supplies a clock signal and changes an oscillating frequency of the supplied clock signal according to an input control voltage; a charge pump into which the clock signal is fed, the charge pump performing a pumping operation in synchronization with the clock signal to boost an input voltage and supply an output voltage in which the input voltage is boosted; a voltage dividing circuit that divides the output voltage of the charge pump to supply a monitor voltage; and a differential amplifier into which the monitor voltage and a reference voltage are fed, the differential amplifier amplifying a potential difference between the monitor voltage and the reference voltage to supply the control voltage.