An objective is to provide a highly-reliable undervoltage lockout circuit which can block and permit normal gate-driver output even when a supply voltage steeply increases. The undervoltage lockout circuit includes a reference-voltage circuit for outputting a reference voltage, a monitor-voltage circuit for outputting a monitor voltage, and a comparator for outputting, the reference voltage and the monitor voltage being inputted thereinto, a high/low signal, according to a comparison result of the reference voltage and the monitor voltage, in which the time constant of the monitor-voltage circuit for determining an increasing rate of the monitor voltage is set higher than that of the reference-voltage circuit for determining that of the reference voltage.