A the harmonica includes a comb having a plurality of cell sets each including four subcells defined by cell walls and airflow partition walls, a plurality of mouthpiece openings disposed upstream or downstream of and registered with the corresponding cell sets in terms of flow of exhaled air or inhaled air, and a reed vibrating member having air passageways registered with the subcells, and a plurality of pairs of reeds registered with the subcells and are vibratile in the corresponding air passageways. When an air flow is evenly introduced into four subcells in one cell set through the corresponding mouth opening as a result of an inhaling or exhaling motion of the player to vibrate the four reeds in the corresponding cell set, four substantially the same notes of diatonic scales are produced.