A spread-spectrum generator is provided. The spread-spectrum generator includes a delay module and a control module. The delay module is controlled by a first control signal to delay an input signal by a delay time, and thereby generate a delay signal. The control module is coupled to the delay module for detecting a first edge of the delay signal, and thereby generating the first control signal. Accordingly, the spread-spectrum generator can spread the frequency of the input signal by delaying the input signal by various delay time, and the spread-spectrum generator can also reduce electromagnetic interference (EMI).