To test the torque control performance while holding the actual speed of a sample side motor at a fixed level, even when a torque command value being given to a sample side motor drive changes abruptly.

A sample side motor drive 20 drives a sample side motor 10 in a torque control mode, a load side motor drive 50 drives a load side motor in a speed control mode, and the sample side motor 10 and the load side motor 40 are coupled by means of a mechanical coupling device 70. A supply side torque command value (1) input to the sample side motor drive 20 is also sent to the torque conversion unit 270 of the load side motor drive 50 and converted into a torque command value suitable for the load side. The torque command value thus converted and the load side torque command value (2) are added by means of an adder 280, and the load side motor 40 is subjected to speed control based on a torque command value obtained as a result of addition.