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 (W2) 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 (L2) 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 (W2) 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 (L2) 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. <EOS>