A booster circuit includes a pump circuit having a plurality of charge pump circuits for outputting a boosted voltage to a first output terminal. The booster circuit also includes a clock adjusting circuit that generates, from a first clock signal, a second clock signal for operating the charge pump circuits. A pump controlling circuit outputs the first clock signal for operating the pump circuit. A first comparator outputs a first output signal. A second comparator outputs a second output signal. A third comparator outputs a third output signal. A gradient of the boosted voltage is decreased when the first output signal is output. A frequency of the first clock signal is reduced when the second output signal is output. The third output signal is output when the boosted voltage is higher than a set value of the boosted voltage.