A music score display data arranging unit provides music score display data for displaying a music score by placing music score notational elements on a given display area in one or more staff tiers, each staff tier containing one or more measures of variable lengths based on inputted music performance representing data. The sizes of the music score notational elements and the size of the display area are determinable. A measures apportioning unit calculates, for each measure based on the sizes of the music score notational elements, a minimum horizontal length for placing at least one kind of notational elements in the measure without an overlap in the horizontal direction, and apportions a number of measures in each staff tier such that the notational elements of each measure shall be placed on the apportioned staff tier in a length of the calculated minimum horizontal length or more.