A coupling system configured to couple a first plate made of a first metal and a second plate made of a second metal to each other, the coupling device comprising: (a) a coupling member ; (b) a first electrode and a second electrode ; (c) a power source connected to the first electrode and the second electrode ; (d) a driver configured to move the first electrode and the second electrode relative to the coupling member , the first plate , and the second plate ; and (e) a controller configured to control the power source and the driver to electrify the coupling member , the first plate , and the second plate while controlling the first electrode and the second electrode to apply pressure to the coupling member , the first plate , and the second plate , wherein the coupling member is made of a third metal identical to the second metal, wherein the first metal has a melting point lower than a melting point of the second metal and a melting point of the third metal, wherein the coupling member comprises a body , a pilot portion provided at a center of a flat surface (51 a) of the body and protruding in an extending direction, and a ring-shaped wall provided along an outer circumference of the flat surface , wherein the pilot portion is solid, wherein the pilot portion , the body , and the ring-shaped wall define a groove space , characterized by the groove space having a first volume equal to or greater than a second volume of a protrusion of the pilot portion , the protrusion protruding from an open surface of the groove space in an outward direction away from the groove space . (a) a coupling member ; (b) a first electrode and a second electrode ; (c) a power source connected to the first electrode and the second electrode ; (d) a driver configured to move the first electrode and the second electrode relative to the coupling member , the first plate , and the second plate ; and (e) a controller configured to control the power source and the driver to electrify the coupling member , the first plate , and the second plate while controlling the first electrode and the second electrode to apply pressure to the coupling member , the first plate , and the second plate , wherein the coupling member is made of a third metal identical to the second metal, wherein the first metal has a melting point lower than a melting point of the second metal and a melting point of the third metal, wherein the coupling member comprises a body , a pilot portion provided at a center of a flat surface (51 a) of the body and protruding in an extending direction, and a ring-shaped wall provided along an outer circumference of the flat surface , a body , a pilot portion provided at a center of a flat surface (51 a) of the body and protruding in an extending direction, and a ring-shaped wall provided along an outer circumference of the flat surface , wherein the pilot portion is solid, wherein the pilot portion , the body , and the ring-shaped wall define a groove space , characterized by the groove space having a first volume equal to or greater than a second volume of a protrusion of the pilot portion , the protrusion protruding from an open surface of the groove space in an outward direction away from the groove space . <EOS>