PURPOSE: To decide whether damping power passes muster or not with high precision, by converting damping power generated by the shock absorber to an electric analogue signal to detect it.

CONSTITUTION: Amplifying circuit 35 converts the analogue signal to signal F proportional to the load, and load signal F of a desired scale is obtained by adjusting variable resistances 35 and 35' of zero balance and gain and is compared with the signal voltage of the rated value in comparing circuit 34 and is converted to a logical signal level. Signals of limit switches 15 and 16 are output from waveform shaping circuit 30, and the output of circuit 34 is held at the output signal rise of circuit 30 by D-FFs 32aW32d of deciding circuit 31, thereby deciding whether damping power passes muster or not. If all output signals of FFs are H level, damping power does not pass muster; but if they are L level, damping power passes muster. When any of FFs is H level, lamp 45 and the lamp of the name corresponding to the rated value for failure are lit. As a result, it is possible to decide whether damping power passes muster or not with a high precision.