There is provided a novel music data compression method which is capable of significantly reducing the size of music data. Music data including a sequence of performance event data each formed of note information is received. Each of the pieces of performance event information of the music data is converted to another form of performance event information including status information corresponding to a matching or mismatching pattern in note information between the piece of performance event information and an immediately preceding one of the pieces of performance event information, and note information necessitated according to the matching or mismatching pattern to which the status information corresponds.