Impact echo method (IEM), which is one of the concrete healthiness test method, is progressive method to measure the rear side cavity of concrete. When measuring IEM, the maximum frequency range generated by the impact devise is determined by its contact time between impact devise and concrete surface. It is known that the maximum frequency range is one of the key parameters to perform IEM precisely and if the frequency range is smaller than the resonance frequency, the result will not be accurate. In this study, the relationship between contact time of impact devises and maximum frequency range was analysed by performing IEM. For the impact devises, impact hammer and steel balls with diameter of 9 mm and 5.9 mm were used. In case of impact hammer, contact time was relatively long and not proper for the thin concrete plate. In case of steel balls, it is observed that the maximum frequency range increases as the diameter of steel ball decreases. It is therefore shown that impact devises should be chosen considering the resonance frequency of the impact object.