1. A method of arranging a target segment of music performance data by means of a template corresponding to an item of music notation to be applied to the target segment, the method comprising the steps of: displaying music performance data on a monitor for designation of a target segment contained in the displayed music performance data and for selection of a specific item of the music notation to be applied to the target segment among various items of the music notation; retrieving a template corresponding to the specific item of the music notation among a group of various templates provisionally prepared in correspondence to the various items of the music notation; customizing the retrieved template to a pitch and a length of the target segment; and rewriting the target segment of the music performance data based on the customized template to thereby arrange the target segment according to the specific item of the music notation.
4. The method according to claim 1, further comprising the step of provisionally preparing a first group of templates applicable to one note and a second group of templates applicable to more than one note, such that the first group can be selected when the target segment contains only one note and the second group can be selected when the target segment contains more than one note.