A mobile device comprising: a main body (100, 310, 700, 10) having a coupling element (121, 321) mounted thereon; and an expansion module electrically connected to the main body, wherein the expansion module comprises: a magnet (221, 221a, 221b, 221c, 221d, 421, 15) disposed to apply a magnetic force to the coupling element (121, 321) to couple the expansion module with the main body (100, 310, 700, 10); and a movement converter configured to move the magnet away from the coupling element so as to decrease the magnetic force between the coupling element (121, 321) and the magnet (221, 221a, 221b, 221c, 221d, 421, 15) thereby decoupling the main body (100, 310, 700, 10) from the expansion module, wherein the movement converter comprises: a manipulation member disposed at a side of the expansion module; and a rotation generator configured to rotate the magnet when the manipulation member is manipulated; characterized in that the movement converter comprises further a sliding generator configured to slide the magnet along an axial direction of a rotation of the magnet when the magnet rotates, and in that the rotation generator comprises: a rotation plate wherein at least part of an outer circumference of the rotation plate is connected to the manipulation member so as to be rotated; and a connection bar having one end connected to the rotation plate and another end connected to a magnet case including the magnet. a main body (100, 310, 700, 10) having a coupling element (121, 321) mounted thereon; and an expansion module electrically connected to the main body, wherein the expansion module comprises: a magnet (221, 221a, 221b, 221c, 221d, 421, 15) disposed to apply a magnetic force to the coupling element (121, 321) to couple the expansion module with the main body (100, 310, 700, 10); and a movement converter configured to move the magnet away from the coupling element so as to decrease the magnetic force between the coupling element (121, 321) and the magnet (221, 221a, 221b, 221c, 221d, 421, 15) thereby decoupling the main body (100, 310, 700, 10) from the expansion module, a magnet (221, 221a, 221b, 221c, 221d, 421, 15) disposed to apply a magnetic force to the coupling element (121, 321) to couple the expansion module with the main body (100, 310, 700, 10); and a movement converter configured to move the magnet away from the coupling element so as to decrease the magnetic force between the coupling element (121, 321) and the magnet (221, 221a, 221b, 221c, 221d, 421, 15) thereby decoupling the main body (100, 310, 700, 10) from the expansion module, wherein the movement converter comprises: a manipulation member disposed at a side of the expansion module; and a rotation generator configured to rotate the magnet when the manipulation member is manipulated; characterized in that the movement converter comprises further a sliding generator configured to slide the magnet along an axial direction of a rotation of the magnet when the magnet rotates, and a manipulation member disposed at a side of the expansion module; and a rotation generator configured to rotate the magnet when the manipulation member is manipulated; characterized in that the movement converter comprises further a sliding generator configured to slide the magnet along an axial direction of a rotation of the magnet when the magnet rotates, and in that the rotation generator comprises: a rotation plate wherein at least part of an outer circumference of the rotation plate is connected to the manipulation member so as to be rotated; and a connection bar having one end connected to the rotation plate and another end connected to a magnet case including the magnet. a rotation plate wherein at least part of an outer circumference of the rotation plate is connected to the manipulation member so as to be rotated; and a connection bar having one end connected to the rotation plate and another end connected to a magnet case including the magnet.