A receptacle connector which is to be mounted and connected to an electronic substrate, comprising: a plurality of signal terminals that can fit together with a plug connector in an extension direction, that are electrically connected to the electronic substrate, and that are configured to transmit signals between a plug connector side and an electronic substrate side; an insulating holder in the form of a circular column that extends in the extension direction and is configured to hold the plurality of signal terminals by being penetrated thereby in the extension direction; a conductive first shell in the form of a tube that covers an outer circumference in a radial direction of the holder; and a non-conductive connector case including a cylindrical space that contains the first shell and extends in the extension direction, the first shell being fixed to the connector case, characterized in that a spacer, which is attached to the first shell from the electronic substrate side, including a surface portion that is orthogonal to the extension direction is included, the surface portion serves as a base on which the electronic substrate is to be mounted; the surface portion includes a support portion having a plurality of insertion holes through which the signal terminals penetrate, a beam portion that supports the support portion, and a spacer engagement hook that protrudes from the surface portion to the plug connector side in the extension direction and has an elastic force along the radius direction, the first shell includes a spacer engagement recessed portion with which the spacer engagement hook engages, on an outer circumferential surface in the radial direction of the first shell, and includes an engagement groove that engages with the beam portion on an end portion on an electronic substrate side in the extension direction, the engagement groove is a cut-out provided along the circumferential direction of the first shell on the end portion on the electronic substrate side of the first shell, the spacer is restricted from moving with respect to the connector case in the extension direction due to the engagement between the spacer engagement hook and the spacer engagement recessed portion, and is restricted from rotating using an axis extending in the extension direction as a rotation axis due to the engagement between the beam portion and the engagement groove, and the spacer restricts rotation of the holder with respect to the connector case in a state in which the signal terminals penetrate through the plurality of insertion holes. a plurality of signal terminals that can fit together with a plug connector in an extension direction, that are electrically connected to the electronic substrate, and that are configured to transmit signals between a plug connector side and an electronic substrate side; an insulating holder in the form of a circular column that extends in the extension direction and is configured to hold the plurality of signal terminals by being penetrated thereby in the extension direction; a conductive first shell in the form of a tube that covers an outer circumference in a radial direction of the holder; and a non-conductive connector case including a cylindrical space that contains the first shell and extends in the extension direction, the first shell being fixed to the connector case, characterized in that a spacer, which is attached to the first shell from the electronic substrate side, including a surface portion that is orthogonal to the extension direction is included, the surface portion serves as a base on which the electronic substrate is to be mounted; the surface portion includes a support portion having a plurality of insertion holes through which the signal terminals penetrate, a beam portion that supports the support portion, and a spacer engagement hook that protrudes from the surface portion to the plug connector side in the extension direction and has an elastic force along the radius direction, the first shell includes a spacer engagement recessed portion with which the spacer engagement hook engages, on an outer circumferential surface in the radial direction of the first shell, and includes an engagement groove that engages with the beam portion on an end portion on an electronic substrate side in the extension direction, the engagement groove is a cut-out provided along the circumferential direction of the first shell on the end portion on the electronic substrate side of the first shell, the spacer is restricted from moving with respect to the connector case in the extension direction due to the engagement between the spacer engagement hook and the spacer engagement recessed portion, and is restricted from rotating using an axis extending in the extension direction as a rotation axis due to the engagement between the beam portion and the engagement groove, and the spacer restricts rotation of the holder with respect to the connector case in a state in which the signal terminals penetrate through the plurality of insertion holes.