A soft start circuit includes a constant current source for generating a constant current, a first current mirror circuit for generating from the constant current a first mirror current, a second current mirror circuit for generating from the constant current a second mirror current smaller than the first mirror current, and a capacitor into which a difference between the first mirror current and the second mirror current is introduced, wherein a divided voltage of a charging voltage thereof is output as a soft start voltage. The soft start circuit provides a gradual soft start voltage.