To solve such a problem (that measuring precision gests worse in a1<a2 when a complex amplitude ratio W=a2/a1 of two waves a2, a1 is found) in a 6-port type correlator of a highly precise and a simple phase measuring system in an ultra-high frequency area and a light area.

This 7-port correlator constituted to be provided with two sets of the 6-port type correlators is provided by adding a reference port of the a2 in addition to a port (reference port) for monitoring an amplitude value of the a1, and the complex amplitude ratio is restricted within a unit circle to realize highly precise measurement, by finding W=a2/a1 in a1≥a2, and by finding W-1=a2/a1 in the a1<a2.