An apparatus for jitter measurement includes a first delay circuit, a second delay circuit, and a control circuit. The first delay circuit imposes a preliminary phase delay on an input signal to generate a delayed input signal. The second delay circuit operates with the first delay circuit to impose a fine phase delay on the delayed input signal. The control circuit controls amounts of delays imposed by the first and second delay circuits, and fine tunes the phase delay of the delayed input signal according to the amounts of delays respectively imposed by delay elements of the first and second delay circuits, and estimates or calculates a jitter window for the input signal according to adjustment results of the first and second delay circuits.