An electrical connector comprising: a housing having a receiving hole; a first contact group and a second contact group, arranged along respective opposite sides of the receiving hole in the housing; and a multilayer circuit board, wherein the first contact group includes a plurality of first signalling contacts being elongate metal terminals extending parallel to an insertion direction and being arranged in a line along a width of the housing, the second contact group includes a plurality of second signalling contacts being elongate metal terminals extending parallel to the insertion direction and being arranged in a line along the width of the housing, at least one of the first and second contact groups further includes a ground contact (220a, 220b) being an elongate metal terminal extending parallel to the insertion direction, and the multilayer circuit board includes: a solid conductor layer provided inside the multilayer board; a first surface being an outer surface of the multilayer circuit board; a second surface being another outer surface of the multilayer circuit board that is opposed to the first surface; first signalling conductors on the first surface of the multilayer circuit board, the first signalling conductors being connected to rear ends of the first signalling contacts; second signalling conductors on the second surface of the multilayer circuit board, the second signalling conductors being connected to rear ends of the second signalling contacts; a ground conductor (322, 332) provided on at least one of the first and second surfaces of the multilayer circuit board; and a via hole connecting between the solid conductor layer and the ground conductor, and the ground conductor of the multilayer circuit board is in contact with the ground contact, characterised in that a leading end of the multilayer circuit board is received in the receiving hole of the housing such as to be interposed between middle portions of the first signalling contacts of the first contact group and middle portions of the second signalling contacts of the second contact group, and a leading end of the solid conductor layer of the multilayer circuit board is interposed between the middle portions of the first signalling contacts of the first contact group and the middle portions of the second signalling contacts of the second contact group. a housing having a receiving hole; a first contact group and a second contact group, arranged along respective opposite sides of the receiving hole in the housing; and a multilayer circuit board, wherein the first contact group includes a plurality of first signalling contacts being elongate metal terminals extending parallel to an insertion direction and being arranged in a line along a width of the housing, the second contact group includes a plurality of second signalling contacts being elongate metal terminals extending parallel to the insertion direction and being arranged in a line along the width of the housing, at least one of the first and second contact groups further includes a ground contact (220a, 220b) being an elongate metal terminal extending parallel to the insertion direction, and the multilayer circuit board includes: a solid conductor layer provided inside the multilayer board; a first surface being an outer surface of the multilayer circuit board; a second surface being another outer surface of the multilayer circuit board that is opposed to the first surface; first signalling conductors on the first surface of the multilayer circuit board, the first signalling conductors being connected to rear ends of the first signalling contacts; second signalling conductors on the second surface of the multilayer circuit board, the second signalling conductors being connected to rear ends of the second signalling contacts; a ground conductor (322, 332) provided on at least one of the first and second surfaces of the multilayer circuit board; and a via hole connecting between the solid conductor layer and the ground conductor, and a ground conductor (322, 332) provided on at least one of the first and second surfaces of the multilayer circuit board; and a via hole connecting between the solid conductor layer and the ground conductor, and the ground conductor of the multilayer circuit board is in contact with the ground contact, characterised in that a leading end of the multilayer circuit board is received in the receiving hole of the housing such as to be interposed between middle portions of the first signalling contacts of the first contact group and middle portions of the second signalling contacts of the second contact group, and a leading end of the solid conductor layer of the multilayer circuit board is interposed between the middle portions of the first signalling contacts of the first contact group and the middle portions of the second signalling contacts of the second contact group. characterised in that a leading end of the multilayer circuit board is received in the receiving hole of the housing such as to be interposed between middle portions of the first signalling contacts of the first contact group and middle portions of the second signalling contacts of the second contact group, and a leading end of the solid conductor layer of the multilayer circuit board is interposed between the middle portions of the first signalling contacts of the first contact group and the middle portions of the second signalling contacts of the second contact group.