A socket for a connector, the socket comprising: a socket-side signal terminal, a socket-side power supply terminal, and a substantially quadrangular socket housing in which the socket-side signal terminal and the socket-side power supply terminal are disposed, wherein the connector comprises a header that has a header-side signal terminal, a header-side power supply terminal, and a substantially quadrangular header housing in which the header-side signal terminal and the header-side power supply terminal are disposed, wherein, by fitting the socket housing and the header housing to each other, the socket-side signal terminal and the header-side signal terminal are brought into contact with each other and the socket-side power supply terminal and the header-side power supply terminal are brought into contact with each other, wherein the socket-side signal terminal and the socket-side power supply terminal are disposed along a long side direction of the socket housing, wherein in the long side direction of the socket housing, the socket-side signal terminal is smaller than the socket-side power supply terminal in width, wherein the socket-side signal terminal and the socket-side power supply terminal have a substantially identical cross-sectional shape, wherein the socket-side power supply terminal is provided with, along the long side direction, a plurality of contacts parts to be brought into contact with a plurality of contact parts of the header-side power supply terminal and wherein the socket-side power supply terminal includes a root part capable of being soldered to a circuit pattern formed at a first circuit board, characterized in that a piece part (35, 36) is respectively formed at each of free end parts (33k, 33m) of the socket-side power supply terminal, wherein said piece parts (35, 36) are respectively provided with the contact parts, in that the plurality of piece parts (35, 36) are flexible, capable of flexing independently and in that the free end parts (33k, 33m) have each an arc-shaped projecting part providing the contact part and adapted to fit into recessed parts of the header-side power supply terminal. a socket-side signal terminal, a socket-side power supply terminal, and a substantially quadrangular socket housing in which the socket-side signal terminal and the socket-side power supply terminal are disposed, wherein the connector comprises a header that has a header-side signal terminal, a header-side power supply terminal, and a substantially quadrangular header housing in which the header-side signal terminal and the header-side power supply terminal are disposed, wherein, by fitting the socket housing and the header housing to each other, the socket-side signal terminal and the header-side signal terminal are brought into contact with each other and the socket-side power supply terminal and the header-side power supply terminal are brought into contact with each other, wherein the socket-side signal terminal and the socket-side power supply terminal are disposed along a long side direction of the socket housing, wherein in the long side direction of the socket housing, the socket-side signal terminal is smaller than the socket-side power supply terminal in width, wherein the socket-side signal terminal and the socket-side power supply terminal have a substantially identical cross-sectional shape, wherein the socket-side power supply terminal is provided with, along the long side direction, a plurality of contacts parts to be brought into contact with a plurality of contact parts of the header-side power supply terminal and wherein the socket-side power supply terminal includes a root part capable of being soldered to a circuit pattern formed at a first circuit board, characterized in that a piece part (35, 36) is respectively formed at each of free end parts (33k, 33m) of the socket-side power supply terminal, wherein said piece parts (35, 36) are respectively provided with the contact parts, in that the plurality of piece parts (35, 36) are flexible, capable of flexing independently and in that the free end parts (33k, 33m) have each an arc-shaped projecting part providing the contact part and adapted to fit into recessed parts of the header-side power supply terminal.