A socket including a socket-side terminal and being configured to be electrically connected to a header including a header-side terminal coming in contact with the socket-side terminal, the socket comprising: a socket housing to which the socket-side terminal is attached, wherein the socket housing as a whole is shaped substantially like a rectangular parallelepiped; and a socket-side retaining fitting attached to the socket housing, wherein the socket housing has a side surface that extends along a width direction of the socket housing as well as a front surface and a rear surface that extend from a bottom surface of the socket housing toward the header along a length direction of the socket housing, wherein the socket-side retaining fitting includes a central portion extending in the width direction of the socket housing and covering the side surface of the socket housing and two arm portions, one of the two arm portions is extending from the central portion to a predetermined position in such a way as to cover part of the front surface of the socket housing and the other of the two arm portions is extending from the central portion to a predetermined position in such a way as to cover part of the rear surface of the socket housing, and two rising portions respectively extending from tip end portions of the two arm portions toward the header, and two locking piece portions respectively being parts continuing to upper end portions of the two rising portions while curving, and configured to respectively lock two locked portions of a header-side retaining fitting attached to the header, and the socket housing includes two covering portions provided in such a way as to respectively cover at least parts of the two locking piece portions, and configured to respectively restrict movements of the two locking piece portions, wherein a lower end portion of each of the two rising portions is configured to be fixed to a circuit board using solder. a socket housing to which the socket-side terminal is attached, wherein the socket housing as a whole is shaped substantially like a rectangular parallelepiped; and a socket-side retaining fitting attached to the socket housing, wherein the socket housing has a side surface that extends along a width direction of the socket housing as well as a front surface and a rear surface that extend from a bottom surface of the socket housing toward the header along a length direction of the socket housing, wherein the socket-side retaining fitting includes a central portion extending in the width direction of the socket housing and covering the side surface of the socket housing and two arm portions, one of the two arm portions is extending from the central portion to a predetermined position in such a way as to cover part of the front surface of the socket housing and the other of the two arm portions is extending from the central portion to a predetermined position in such a way as to cover part of the rear surface of the socket housing, and two rising portions respectively extending from tip end portions of the two arm portions toward the header, and two locking piece portions respectively being parts continuing to upper end portions of the two rising portions while curving, and configured to respectively lock two locked portions of a header-side retaining fitting attached to the header, and the socket housing includes two covering portions provided in such a way as to respectively cover at least parts of the two locking piece portions, and configured to respectively restrict movements of the two locking piece portions, wherein a lower end portion of each of the two rising portions is configured to be fixed to a circuit board using solder.