A display area, in which a note is displayed on two-axis coordinates configured by a tone pitch axis and a time axis, is displayed on a display device. A display magnification ratio used in the display area is variable. A note image of a given note is displayed in the display area to be arranged in correspondence with a tone pitch and a tone generation time of the note. The size of the note image is varied with the display magnification ratio. Relevant information is displayed in association with the note image displayed in the display area in such a manner that the relevant information is arranged inside the note image of the note in a first display state and the relevant information is arranged outside the note image of the note in a second display state with a display magnification ratio lower than that of the first display state.