Performances of two skilled amateur pianists were analyzed to investigate factors deter mining the impression of the equality of intensity in piano music. The results of the analysis showed that although the pianists tried to play every tone as equally as possible, not all the tones were played in equal intensity. The following two features were found in the performances:(1) The pattern of fluctuation was regularly repeated throughout the performance.(2) The peak level of each “playing unit” was remarkably kept constant compared with the fluctuation of each tone. The same tendency was also found in the performances of professional pianists. The results of the psychoacoustical experiment showed that when these features were destroyed, the impression of equality was degraded. These findings suggest that skilled pianists can maintain the impression of the equality of intensity by making good use of the characteristics of our auditory perception.