A portable device comprising: an at least one body (100, 42, 52, 54, 62, 64, 72, 74, 210); a variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75) which is assembled at a predetermined location of the at least one body and configured to slide up/down in a longitudinal direction with respect to the at least one body according to antenna reception sensitivity, wherein the variable built-in antenna senses its reception sensitivity and slides upward or downward with respect to the at least one body according to the sensed reception sensitivity, wherein the variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75) comprises an antenna housing which comprises an edge portion, first and second side portions (302, 303), and a rear portion to cover a predetermined portion of the at least one body (100, 42, 52, 54, 62, 64, 72, 74, 210) such that the antenna housing slides in a longitudinal direction of the at least one body while facing the at least one body, wherein the variable built-in antenna designates an antenna unit of which reception sensitivity varies according to whether the antenna unit installed in the antenna housing is slid upward/down; and an electrical connection device (82, 90) for signal transmission between the at least one body and the variable built-in antenna, configured to slide up/down with respect to the at least one body (100, 42, 52, 62, 72, 210), wherein the electrical connection device (82, 90) comprises: a fixed printed circuit board, PCB, mounted on the at least one body; a mobile antenna PCB mounted on the variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75); and wherein the connection device (82, 90) is configured to transmit signals by connecting an end to the fixed PCB and connecting an end to the mobile antenna PCB, wherein a length of the connection device varies according to a sliding movement of the mobile antenna PCB. an at least one body (100, 42, 52, 54, 62, 64, 72, 74, 210); a variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75) which is assembled at a predetermined location of the at least one body and configured to slide up/down in a longitudinal direction with respect to the at least one body according to antenna reception sensitivity, wherein the variable built-in antenna senses its reception sensitivity and slides upward or downward with respect to the at least one body according to the sensed reception sensitivity, wherein the variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75) comprises an antenna housing which comprises an edge portion, first and second side portions (302, 303), and a rear portion to cover a predetermined portion of the at least one body (100, 42, 52, 54, 62, 64, 72, 74, 210) such that the antenna housing slides in a longitudinal direction of the at least one body while facing the at least one body, wherein the variable built-in antenna designates an antenna unit of which reception sensitivity varies according to whether the antenna unit installed in the antenna housing is slid upward/down; and an electrical connection device (82, 90) for signal transmission between the at least one body and the variable built-in antenna, configured to slide up/down with respect to the at least one body (100, 42, 52, 62, 72, 210), wherein the electrical connection device (82, 90) comprises: a fixed printed circuit board, PCB, mounted on the at least one body; a mobile antenna PCB mounted on the variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75); and wherein the connection device (82, 90) is configured to transmit signals by connecting an end to the fixed PCB and connecting an end to the mobile antenna PCB, wherein a length of the connection device varies according to a sliding movement of the mobile antenna PCB. a fixed printed circuit board, PCB, mounted on the at least one body; a mobile antenna PCB mounted on the variable built-in antenna (300, 40, 50, 55, 60, 65, 70, 75); and wherein the connection device (82, 90) is configured to transmit signals by connecting an end to the fixed PCB and connecting an end to the mobile antenna PCB, wherein a length of the connection device varies according to a sliding movement of the mobile antenna PCB.