To easily judge whether or not the input signal is suitable for input data by converting the output data of logic simulator into level data corresponding to the numerical values and by changing over/indicating them and respective signals of data bus to be inputted to a simulator, on a waveform indicating part.

A circuit 10 to be tested that is of digital/analog mixing LSI is comprised of a logic circuit 11 and a conversion part (DAC) 12 for converting its output into analog signal. In a waveform indicating device 40 which indicates the I/O waveform of a logic simulator 30, a level conversion part 41 converts a digital input signal into an analogic level signal, and a switching part 42 changes over the digital input signal and level signal and outputs them, then an indicating part 43 indicates them on the screen. Thus, the conversion part 41 forms the input signal into a horizontal line according to its numerical value and indicates a psuedo analog indication, so that it can be easily judged whether or not the input signal is suitable for the input data of the DAC 12.