A connector (1, 110, 120, 130) comprising: an elastic valve body (3, 300) which includes a top face on which a slit is formed and a bottom face on an opposite side of the top face; a holding section which is provided with an annular top-face-side holding section which is configured to engage a first engaging projection of a top face cap of a housing of the connector (1, 110, 120, 130) and in contact with the top face of the elastic valve body (3, 300), and an annular bottom-face-side holding section which is configured to engage a second engaging projection of a bottom cap of said housing of the connector (1, 110, 120, 130) and in contact with the bottom face, compresses and holds the elastic valve body (3, 300) together with the top-face-side holding section; and wherein the elastic valve body (3, 300) includes a constricted section which is held by the holding section; wherein the holding section is provided to surround the slit, and the elastic valve body (3, 300) includes a peripheral section which is positioned on an outer side than the constricted section when the elastic valve body (3, 300) is viewed from the top face side, and characterized in that the peripheral section on both the top face side and the bottom face side is thicker than the constricted section; a volume of the peripheral section in a state in which the elastic valve body (3, 300) is held by the holding section is larger than a volume of the peripheral section in a state in which the elastic valve body (3, 300) is not held by the holding section; and wherein an outer diameter of the elastic valve body (3, 300) in the section parallel to the radial direction A including the constricted section in the state of being held by the holding section is larger than the outer diameter of the elastic valve body (3, 300) in the section parallel to the radial direction A including the constricted section in the state of not being held by the holding section; and said housing includes an inner wall section (52, 520) that surrounds the perimeter of the elastic valve body (3, 300) in a more radial direction of the elastic valve body (3, 300) on an outer side in the radial direction than the peripheral section; a gap is provided between the peripheral section and the inner wall section (52, 520) in the state in which the elastic valve body (3, 300) is held by the holding section. an elastic valve body (3, 300) which includes a top face on which a slit is formed and a bottom face on an opposite side of the top face; a holding section which is provided with an annular top-face-side holding section which is configured to engage a first engaging projection of a top face cap of a housing of the connector (1, 110, 120, 130) and in contact with the top face of the elastic valve body (3, 300), and an annular bottom-face-side holding section which is configured to engage a second engaging projection of a bottom cap of said housing of the connector (1, 110, 120, 130) and in contact with the bottom face, compresses and holds the elastic valve body (3, 300) together with the top-face-side holding section; and wherein the elastic valve body (3, 300) includes a constricted section which is held by the holding section; wherein the holding section is provided to surround the slit, and the elastic valve body (3, 300) includes a peripheral section which is positioned on an outer side than the constricted section when the elastic valve body (3, 300) is viewed from the top face side, and characterized in that the peripheral section on both the top face side and the bottom face side is thicker than the constricted section; a volume of the peripheral section in a state in which the elastic valve body (3, 300) is held by the holding section is larger than a volume of the peripheral section in a state in which the elastic valve body (3, 300) is not held by the holding section; and wherein an outer diameter of the elastic valve body (3, 300) in the section parallel to the radial direction A including the constricted section in the state of being held by the holding section is larger than the outer diameter of the elastic valve body (3, 300) in the section parallel to the radial direction A including the constricted section in the state of not being held by the holding section; and said housing includes an inner wall section (52, 520) that surrounds the perimeter of the elastic valve body (3, 300) in a more radial direction of the elastic valve body (3, 300) on an outer side in the radial direction than the peripheral section; a gap is provided between the peripheral section and the inner wall section (52, 520) in the state in which the elastic valve body (3, 300) is held by the holding section.