PURPOSE: To eliminate the need to operate a testing machine actually even when a program is modified by providing an equivalent circuit which has the same transfer function with a testing machine system and connecting the equivalent circuit to a computer through a changeover switch.

CONSTITUTION: When whether the program has a bug or not and the operation characteristics of the testing machine are checked in the modification of the program, the changeover switch 7 is switched to the equivalent circuit and the computer 1 is put in operation to observe a monitor 9. When it is evident on the display of the monitor 90 that the computer does not operate according to the contents of the program, it is checked whether the program has a bug or not. The program is corrected and executed again by the computer 1, and the current operation characteristics are recorded. Thus, the checks are made and the changeover switch 7 is switched to a hydraulic operation type testing machine 3 and a test-piece 4 is set and tested actually according to the modified program. Data obtained at this time are compared with said operation characteristics to discriminate an error base, thereby investigating the data.