An electronic device, comprising: a housing comprising a first plate, a second plate facing away from the first plate, and a side member surrounding a space between the first plate and the second plate, wherein the side member comprises a first conductive portion, a first non-conductive portion, a second conductive portion, a second non-conductive portion, and a third conductive portion sequentially disposed, and wherein the second plate is formed of a conductive material, and comprises a first conductive region, a second conductive region, a third conductive region and a non-conductive slit surrounding the first conductive region together with the second conductive portion when viewed from an upper side of the second plate, the non-conductive slit extending from the first non-conductive portion to the second non-conductive portion; a touch screen display disposed within the housing and exposed through a portion of the first plate; a printed circuit board, PCB, disposed between the first plate and the second plate, wherein the PCB comprises a main ground plane and a first L-shaped ground extension disposed between the first conductive region of the second plate and the first plate, and the first L-shaped ground extension comprises a first portion extending generally in a second direction from the main ground plane and a second portion extending generally in a first direction perpendicular to the second direction from the first portion; at least one first wireless communication circuit disposed on the PCB and electrically connected to a first point in the second portion of the first L-shaped ground extension; and a switching device configured to change an electrical length of a slit formed by the second portion of the first L-shaped ground extension and the main ground plane by selectively connecting the second portion of the first L-shaped ground extension and the main ground plane. a housing comprising a first plate, a second plate facing away from the first plate, and a side member surrounding a space between the first plate and the second plate, wherein the side member comprises a first conductive portion, a first non-conductive portion, a second conductive portion, a second non-conductive portion, and a third conductive portion sequentially disposed, and wherein the second plate is formed of a conductive material, and comprises a first conductive region, a second conductive region, a third conductive region and a non-conductive slit surrounding the first conductive region together with the second conductive portion when viewed from an upper side of the second plate, the non-conductive slit extending from the first non-conductive portion to the second non-conductive portion; a touch screen display disposed within the housing and exposed through a portion of the first plate; a printed circuit board, PCB, disposed between the first plate and the second plate, wherein the PCB comprises a main ground plane and a first L-shaped ground extension disposed between the first conductive region of the second plate and the first plate, and the first L-shaped ground extension comprises a first portion extending generally in a second direction from the main ground plane and a second portion extending generally in a first direction perpendicular to the second direction from the first portion; at least one first wireless communication circuit disposed on the PCB and electrically connected to a first point in the second portion of the first L-shaped ground extension; and a switching device configured to change an electrical length of a slit formed by the second portion of the first L-shaped ground extension and the main ground plane by selectively connecting the second portion of the first L-shaped ground extension and the main ground plane.