An earphone (1) includes a cylindrical barrel (2) having one end thereof inserted in an ear canal, a transmission element (4) that is provided on a part of the side of the barrel (2), has a part thereof being in contact with a tragus of a human body while the barrel (2) is inserted in the ear canal and has a built-in electroacoustic conversion element (3) configured to generate an acoustic vibration in response to an electrical signal, a vibration element (5) that is provided on an inner wall of the barrel (2) and vibrates in reaction to the acoustic vibration from the electroacoustic conversion element (3), and a biosensor (30).