The relationship between the reduction of friction coefficient by the acoustic pressure and deflection vibration, and the particle density has been shown when ultrasonic was applied for two parallel plates and 7 kinds of particles. Additionally, the maximum of particle density which could receive the friction reduction effect by the acoustic pressure has been expressed. In this study, in order to evaluate the effect by them, the distribution of acoustic pressure between reflection plate and the vibration plate by the acoustic pressure have been measured. As a result, it was clear that acoustic pressure distribution became the almost same whether ultrasonic was applied for the either plate, and the reflection plate vibrate little. Therefore it was possible to divide the influence of acoustic pressure and deflection vibration on the friction reduction.