To provide a method and an apparatus capable of measuring phase noises with lower levels in comparison with conventional ones.

In the method, a first phase signal representing a phase of a signal to be measured is generated by using a first local signal which is generated by referring to a first reference signal, and a second phase signal representing another phase of the signal to be measured by using a second local signal which is generated by referring to a second reference signal having a frequency different from that of the first reference signal, and then a cross-correlation or a cross spectrum between the first phase signal and the second phase signal is obtained, thereby measuring the phase noises of the signal to be measured. Furthermore, the apparatus measures the phase noises of the signal to be measured by using the above method.