An acoustic apparatus using a bone-conduction speaker can eliminate a sound pressure type speaker heretofore required and permit a bone-conduction speaker to serve both in communication and in outputting an incoming tone, thus reducing the apparatus in size and weight. The apparatus comprises: an outer casing (3), in which a bone-conduction speaker is incorporated; a unit case (1) mounted in the outer casing (3) through a support means (4); a drive means (5) for displacing the unit case (1) in the outer casing (3), the drive means (5) being disposed in the outer casing (3); an opening formed in the outer casing (3) in a manner such that the unit case (1) is permitted to have its side-head abutting surface (2) exposed to the outside, wherein the drive means (5) is so operated as to have the unit case (1) brought into or out of contact with the outer casing (3).