To derive a correlation equation for particle collision frequency with an impeller, the influence on the collision frequency of operational conditions such as impeller speed, particle size and solid-liquid density difference was examined based on a collision detection method using wavelet analysis. It was found that the particle often collided with the impeller at a time interval of several tens of milliseconds. In addition, the relation between the collision frequency and operational conditions was confirmed to depend on a threshold. which is set to detect the collisions. Therefore, the correlation equation was derived as a function of the threshold by experimentally establishing a model in which collision sound pressure has a log-normal distribution independently of operational conditions. Further, it was shown that the correlation equation could estimate collision frequency as a function of collision energy by establishing a relation between the threshold and the collision energy in future.