PURPOSE: To make it possible to measure the load torque under the mounted state by driving a stepping motor in actual measurement, and measuring the actual load torque based on the frequency when step-out is generated and the frequency versus pull-out torque characteristic.

CONSTITUTION: A switch 9 is connected to a terminal S2. A stepping motor 1 is coupled to an actual-machine mechanism part 2 through a coupling 3. A frequency undergoes slow-up control based on a control signal from a (slow-up- and-down) stepping controller 5. Thus, the motor 1 is driven by a motor driver 4. When the number of rotation is gradually increased, the motor 1 steps out at a certain frequency, and the step-out 6 is detected. When the motor 1 steps out at a point on a reference pull-out-torque curve, the detected step-out signal (a) is sent from a step-out detecting part 6 into a load-torque measuring part 10B. The slow-up frequency at this time is latched. The pull-out torque at the frequency is sent into an output device 11 as the load torque based on the detected step-out signal and the reference curve data from a pull-out-curve processing and memory part 10A with the load-torque measuring part 10B.