PURPOSE: To display the waveform of a phenomenon on an oscilloscope face by displaying a signal waveform on the tube face in the manner of sending outputs from a trigger circuit and an adding circuit to input signal terminals of the oscilloscope.

CONSTITUTION: The oscilloscope 10 consists of a knob for providing a horizontal axis to settle a time value of the tube face display signal, knob for providing a vertical axis to settle tube face waveforms possible to display two channels, probe for detecting the signal to induce a measured signal from an automobile machine, and, etc. The trigger level is adjusted by a trigger adjusting knob. The adding circuit 30, trigger circuit 40 and microcomputer 60 are provided in the operation aiding device 1 for the oscilloscope. The signal come from the probe 15 is inputted to a resistor 32 side in the circuit 30 and the output side of which is connected to the signal input terminals of the oscilloscope 10. In the circuit 40, a pulse signal is automatically detected by the input signal come from the probe 15, and the detected signal is sent out to the oscilloscope 10 and a data processor respectively. The actual waveform of the phenomenon can be thereby displayed on the tube face of the oscilloscope 10.