The acoustic impedance of a perforated plate varies with the magnitude of sound pressure; the acoustic resistance depends on the particle velocity through its holes. We measured the acoustic impedance of perforated plates with porosity of 0.025 - 0.234 at the sound pressure level up to about 150dB, and compared the results with the values predicted by use of the formula proposed by Guess. Wide frequency range sound and single frequency sound were used for the measurement. The particle velocity was estimated from the sound pressure and measured acoustic impedance. When the particle velocity is comparatively high, the acoustic resistance linearly increases with the particle velocity as it appears in Guess's formula. The measured gradient agrees with the value expressed in Guess's formula if the Mach number defined as the root mean square value of the estimated particle velocity divided by the sound speed is applied.