A chord-playing input device characterized by comprising: a plurality of chord designating buttons (3, 3A to 3I) arranged on a casing and assigned respectively with chords; a plurality of chord changing buttons (4, 4A to 4K) arranged on the casing side by side with the chord designating buttons (3, 3A to 3I) and assigned respectively with change methods for changing an assignment state of the chords for the chord designating buttons (3, 3A to 3I); and a sounding information generating part that generates sounding information for making a sounding part emit a sound of the chord corresponding to operation for any of the chord designating buttons (3, 3A to 3I) and chord changing buttons (4, 4A to 4K); wherein the plurality of chord designating buttons (3, 3A to 3I) are each assigned with a first root and a first chord type that constitute the chord, at least one of the plurality of chord changing buttons (4, 4A to 4K) is assigned with, as the change method, mutually different third and fourth chord types to change the assignment state, characterized by a display information generating part that generates display information for making a display part display a plurality of chord images (900A to 9001) which are written chord names comprising root and chord type representing the chords assigned respectively to the chord designating buttons (3, 3A to 3I) and a plurality of change method images (901A to 901K) which are the change methods in writing assigned respectively to the chord changing buttons (4, 4A to 4K) in the same arrangement order as those of the chord designating buttons (3, 3A to 3I) and chord changing buttons (4, 4A to 4K), wherein when the first chord type corresponds to the third chord type, the first chord type is replaced with the fourth chord type to change the assignment state, while when the first chord type corresponds to the fourth chord type, the first chord type is replaced with the third chord type to change the assignment state, the third chord type and the fourth chord type are replaced with each other by one operation for the chord changing button. a plurality of chord designating buttons (3, 3A to 3I) arranged on a casing and assigned respectively with chords; a plurality of chord changing buttons (4, 4A to 4K) arranged on the casing side by side with the chord designating buttons (3, 3A to 3I) and assigned respectively with change methods for changing an assignment state of the chords for the chord designating buttons (3, 3A to 3I); and a sounding information generating part that generates sounding information for making a sounding part emit a sound of the chord corresponding to operation for any of the chord designating buttons (3, 3A to 3I) and chord changing buttons (4, 4A to 4K); wherein the plurality of chord designating buttons (3, 3A to 3I) are each assigned with a first root and a first chord type that constitute the chord, at least one of the plurality of chord changing buttons (4, 4A to 4K) is assigned with, as the change method, mutually different third and fourth chord types to change the assignment state, characterized by a display information generating part that generates display information for making a display part display a plurality of chord images (900A to 9001) which are written chord names comprising root and chord type representing the chords assigned respectively to the chord designating buttons (3, 3A to 3I) and a plurality of change method images (901A to 901K) which are the change methods in writing assigned respectively to the chord changing buttons (4, 4A to 4K) in the same arrangement order as those of the chord designating buttons (3, 3A to 3I) and chord changing buttons (4, 4A to 4K), wherein when the first chord type corresponds to the third chord type, the first chord type is replaced with the fourth chord type to change the assignment state, while when the first chord type corresponds to the fourth chord type, the first chord type is replaced with the third chord type to change the assignment state, the third chord type and the fourth chord type are replaced with each other by one operation for the chord changing button.