A nonlinear distortion is compensated based upon a characteristic relating to a characteristic of a device under test. An inverse characteristic measuring device measures an output signal output from the device under test as a result of supplying the device under test with an input signal generated by a signal source. Further, the inverse characteristic measuring device acquires an ideal signal output from the device under test based upon the input signal if the device under test is ideal. Moreover, the inverse characteristic measuring device acquires an inverse characteristic which is a relation of the ideal signal with respect to the output signal. This inverse characteristic is applied to a distortion compensator. The distortion compensator supplies the device under test with the input signal converted based upon the inverse characteristic. As a result, a signal output from the device under test is an ideal signal whose distortion caused by the device under test is compensated.