A plug for being inserted in a jack of an external apparatus which includes a noise cancel signal production section and a reproduction section to establish connection of first and second microphones (6, 8) and first and second speakers (7, 9) provided in a sound inputting and outputting apparatus to the external apparatus, the plug comprising: a first conductor configured to transmit a first noise signal to the external apparatus in response to first noise inputted to the first microphone; a second conductor configured to transmit a second noise signal to the external apparatus in response to second noise inputted to the second microphone; a third conductor configured to transmit a first synthesis signal of a first noise cancel signal produced by the noise cancel signal production section in response to the first noise signal and a first sound signal reproduced by the reproduction section to the first speaker; a fourth conductor for grounding; and a fifth conductor configured to transmit a second synthesis signal of a second noise cancel signal produced by the noise cancel signal production section in response to the second noise signal and a second sound signal reproduced by the reproduction section to the second speaker; wherein said first conductor includes an electrode portion and a fitting portion and is formed like a round bar; said second conductor includes an electrode portion and a fitting portion; said third conductor includes an electrode portion and a fitting portion; said fourth conductor includes an electrode portion; said plug further includes: a first insulator outwardly fitted on said fitting portion of said first conductor to isolate said first and second conductors from each other; a second insulator outwardly fitted on said fitting portion of said second conductor to isolate said second and third conductors from each other; a third insulator outwardly fitted on said fitting portion of said third conductor to isolate said third and fourth conductors from each other; and a fourth insulator attached to at least part of an outer face of said fourth conductor; and said fifth conductor is attached to but isolated from said fourth insulator. a first conductor configured to transmit a first noise signal to the external apparatus in response to first noise inputted to the first microphone; a second conductor configured to transmit a second noise signal to the external apparatus in response to second noise inputted to the second microphone; a third conductor configured to transmit a first synthesis signal of a first noise cancel signal produced by the noise cancel signal production section in response to the first noise signal and a first sound signal reproduced by the reproduction section to the first speaker; a fourth conductor for grounding; and a fifth conductor configured to transmit a second synthesis signal of a second noise cancel signal produced by the noise cancel signal production section in response to the second noise signal and a second sound signal reproduced by the reproduction section to the second speaker; wherein said first conductor includes an electrode portion and a fitting portion and is formed like a round bar; said second conductor includes an electrode portion and a fitting portion; said third conductor includes an electrode portion and a fitting portion; said fourth conductor includes an electrode portion; said plug further includes: a first insulator outwardly fitted on said fitting portion of said first conductor to isolate said first and second conductors from each other; a second insulator outwardly fitted on said fitting portion of said second conductor to isolate said second and third conductors from each other; a third insulator outwardly fitted on said fitting portion of said third conductor to isolate said third and fourth conductors from each other; and a fourth insulator attached to at least part of an outer face of said fourth conductor; and a first insulator outwardly fitted on said fitting portion of said first conductor to isolate said first and second conductors from each other; a second insulator outwardly fitted on said fitting portion of said second conductor to isolate said second and third conductors from each other; a third insulator outwardly fitted on said fitting portion of said third conductor to isolate said third and fourth conductors from each other; and a fourth insulator attached to at least part of an outer face of said fourth conductor; and said fifth conductor is attached to but isolated from said fourth insulator.