It is possible to apply a correct power to a load even when the output
impedance and a load impedance of a signal source are different from a
characteristic impedance of a transmission line. The power applied to the
load can be expressed by a measurement system error factor, a load
coefficient X of the load, and an S parameter of the input signal R.
Accordingly, a target input signal decision can decide a target value of
the S parameter of the input signal R according to the power desired to
be applied to the load, the measurement system error factor, and the load
coefficient X of the load. Furthermore, an input signal level control
section controls the input signal level so that the S parameter of the
input signal R has this target value. This is performed by changing the
amplification ratio of an amplification ratio variable amplifier. Thus,
it is possible to apply a desired power to the load not depending on
whether the impedance is matched or not.