To solve the problems that errors occur in an engine torque estimated value due to the pulsation of an engine, which is load, to affect the torque command values of a dynamometer when simulating load in an engine bench system and that accurate simulation can not be executed.

A detected shaft torque signal Ted and the velocity signals ωd and ωe of the dynamometer or the engine are introduced to an engine torque observer and are outputted as a torque estimated value Tco by performing the following computation at the observer. Teo(s)=GTed(s)Ted(s)+Gωe(s)ωe(s), or Teo(s)=GTed(s)Ted(s)+Gωd(s)ωd(s).