To provide a phase difference detecting circuit which can detect a signal having a large phase difference, such as the wander of a high-frequency signal, with high resolution by means of a lower-speed circuit element by constituting the circuit by combining a low-speed phase counting circuit with a high- resolution phase counting circuit, and a method for detecting phase difference.

The phase difference detecting circuit detects the phase-counted result corresponding to the phase difference detected by means of a phase comparator circuit 2 and a phase counting circuit 3 and the phase difference, which has not been detected by means of the counting circuit 3, with high resolution by means of a high-resolution phase counting circuit 5 of the poststage. Thereby, the circuit 1 which can operate at a frequency lower than that of a received extracted clock signal inputted from a transmission system to be measured can be realized.