There are provided a circuit and a method for detecting a duty ratio of a PWM signal. The circuit includes: a counting unit counting a PWM signal; a detection indication determining unit determining whether a detection indication signal indicating a start of detection of the duty ratio of the PWM signal has been input; an edge detecting unit detecting a preset PWM edge of the PWM signal; and a duty calculating unit calculating the duty ratio of the PWM signal using a count value during a section from a k-th point in time (T(k)) (k being a natural number of 1 or more) at which the PWM edge is detected after it is determined that the detection indication signal has been input to a k+1-th point in time (T(k+1)) at which the PWM edge is detected after it is subsequently determined that the detection indication signal has been input.