To extract simply an interference wave component signal from a modurated wave signal and to measure constantly and adequately interference amount without using any empty channel.

The estimating instrument consists of an interference power estimating means which calculates the power signal of interference wave component extracted from a specifically modurated wave signal containing desirable signal wave component and interference wave component inputted from an input terminal 1 and outputs the interference power signal, an input power estimating means which calculates the power of the modurated wave signal and outputs the input power signal derived from it, and an interference amount calculator 11 which calculates the interference amount on the basis of the interference power signal and the input power signal and outputs the interference amount signal to an output terminal 12. In the interference power estimating mean, a judging device 2 judges and extracts signal wave component from the modurated wave signal and outputs its data signal, and a complex subtracter 6 extracts interference wave component with subtraction of the modurated wave signal and the data signal changed in amplitude so that the data signal has the same amplitude as that of modurated wave signal.