An inserting body of an earphone device, said inserting body comprising a retainer (10; 10A; 10B; 10C; 10D; 10E; 10F; 10G; 10H; 10J; 10K; 10L; 10M; 10N; 10R; 10S) connectable to a signal-to-sound converter (20; 20C; 20J; 20L; 20M; 20N; 20R; 20S), engaged with at least one external ear of said human being and forming an internal sound propagation path (11; 11A) for propagating internal sound from said signal-to-sound converter (20; 20C; 20J; 20L; 20M; 20N; 20R; 20S) to at least one external auditory meatus of a human being and an external sound propagation path (13; 13A; 13B; 13H) open at one end thereof to an environment and at the other end thereof to said at least one external auditory meatus for propagating external sound, and an actuator (12; 12A; 12B; 12C; 12D; 12E; 12J; 12K; 12L; 12M; 12N; 12R; 12S; 122a/ 112b/ 122c/ 122d; 123a/ 123b/ 123c/ 123d; 124a/ 124b/ 124c/ 124d) connected to said retainer (10; 10A; 10B; 10C; 10D; 10E; 10F; 10G; 10H; 10J; 10K; 10L; 10M; 10N; 10R; 10S) and responsive to voltage applied thereto so as to be deformed for closing said external sound propagation path (13; 13A; 13B; 13H) therewith and permitting said environment to be conducted to said external auditory meatus through said external sound propagation path (13; 13A; 13B; 13H), characterized in that said actuator (12; 12A; 12B; 12C; 12D; 12E; 12J; 12K; 12L; 12M; 12N; 12R; 12S; 122a/ 112b/ 122c/ 122d; 123a/ 123b/ 123c/ 123d; 124a/ 124b/ 124c/ 124d) is formed from conductive layers (12f/ 12h) applied with said voltage and a polymer layer sandwiched between said conductive layers (12f/ 12h) and deformable with said voltage applied thereto through said conductive layers (12f/ 12h); wherein said external sound propagation path (13; 13A) is defined by an inner surface of said retainer (10; 10A; 10B; 10C; 10D; 10E; 10F; 10G; 10H; 10J; 10K; 10L; 10M; 10N 10R; 10S) so as to be formed inside said retainer (10; 10A; 10B; 10C; 10D; 10E; 10F; 10G; 10H; 10J; 10K; 10L; 10M; 10N; 10R; 10S); and wherein: said actuator (12; 12C; 122a/ 122b/ 122c/ 122d; 123a/ 123b/ 123c/ 123d; 12J; 12K; 12L; 12M; 12N; 12R; 12S) is provided in said external sound propagation path (13; 13A) so as to be spaced from said inner surface for making said external sound conducted to said at least one external auditory meatus and brought into contact with said inner surface for closing said external sound propagation path (13; 13A), or said actuator (12A; 12D) is formed on an outer wall of said retainer (10A; 10D) around an sound outlet port (130a/ 130b/ 130c/ 130d) of said external sound propagation path so as to be spaced from an outer surface of said outer wall for making said external sound conducted to said at least one external auditory meatus and brought into contact with said outer surface for closing said external sound propagation path. an internal sound propagation path (11; 11A) for propagating internal sound from said signal-to-sound converter (20; 20C; 20J; 20L; 20M; 20N; 20R; 20S) to at least one external auditory meatus of a human being and an external sound propagation path (13; 13A; 13B; 13H) open at one end thereof to an environment and at the other end thereof to said at least one external auditory meatus for propagating external sound, and said actuator (12; 12C; 122a/ 122b/ 122c/ 122d; 123a/ 123b/ 123c/ 123d; 12J; 12K; 12L; 12M; 12N; 12R; 12S) is provided in said external sound propagation path (13; 13A) so as to be spaced from said inner surface for making said external sound conducted to said at least one external auditory meatus and brought into contact with said inner surface for closing said external sound propagation path (13; 13A), or said actuator (12A; 12D) is formed on an outer wall of said retainer (10A; 10D) around an sound outlet port (130a/ 130b/ 130c/ 130d) of said external sound propagation path so as to be spaced from an outer surface of said outer wall for making said external sound conducted to said at least one external auditory meatus and brought into contact with said outer surface for closing said external sound propagation path.