The present invention discloses a soft-start circuit having a reference signal generator, a first current generator, a second current generator, and a soft-start capacitor. The reference signal generator generates a first signal and a second signal. The first current generator generates a first current according to the first signal, and the second current generator generates a second current according to the second signal. The soft-start capacitor is coupled to the first current generator and the second current generator, and charged by a current difference of the first current and the second current to generate a soft-start signal.