The application methods in the related art cannot apply a sufficient voltage with a rectangular wave having a short rise time to an electronic circuit. Furthermore, electrostatic discharge test can apply a sufficient voltage but can only apply an oscillating waveform.A TLP generator is used as a rectangular wave generator. The sum of an injection resistance and a matching resistance is set so as to match the characteristic impedance of a transmission line for transmitting a rectangular wave to a test target. A capacitor is connected to a return line of the applied rectangular wave. With this configuration, stable application can be achieved. An error observation function of an electronic circuit gradually increases a peak value of the rectangular wave and determines the immunity based on an application voltage to cause an error for the first time.