To measure the waveform of the frequency component of arbitrary frequency component contained in the engine generating torque and the waveform of the engine generating torque in a high accuracy.

In the engine testing apparatus which carries out the torque control of the dynamometer 2 by the output torque sensing of the engine 1; an engine generating torque estimator 10 performs sine conversion and cosine conversion of the output torque detected signal on the frequency (f) with multipliers 16 and 17, passes these signals to the low pass filters 18, 19 (or an integrator), respectively, and extracts only the sine element and the cosine element of the frequency (f) which are contained in the engine generating torque. These are performed in reverse sine conversion and reverse cosine conversion with multipliers 20 and 21, respectively, and it composes with an adder 24, and the waveform of the frequency (f) element is acquired about engine generating torque. A function generator 26 compensates phase lag and gain fall off. It includes that the provision of the presuming sections 10 for the frequency f to f×N parts.