To instantly determine whether or not a servo-type testing device is operated ideally.

An input Ei that increases monotonously is inputted from a function generator 1 and servo control is made, so that a displacement speed becomes constant with the output of a displacement-measuring instrument 25 as a control variable. A sample piece 22 is compressed by a servo valve 22 and an actuator 23, and the displacement and load are measured by the displacement-measuring instrument 25 and a load-measuring instrument 24. A signal corresponding to displacement and load sampled by A/D converts 32 and 33 according to a sampling clock CL with a prescribed period, is converted into a digital signal, and is inputted to an output device 34, thus outputting the load-displacement curve of a test piece 21. The output is expressed by a row of discrete pints with an interval corresponding to the period of the sampling clock CL, thus instantly determining whether or not a servo system is operated ideally, depending on whether or not the displacement of each point is at a constant interval.