A module assembly comprising a plurality of modules (10, 20, 30, 40), wherein the plurality of modules (10, 20, 30, 40) comprises a first module and a second module, the first module and the second module each including a terminal configured to transfer at least one of electric energy, electric signals and data, and the terminal of the first module being in contact with the terminal of the second module when the first module is coupled to the second terminal, wherein each of the first and second modules comprises: a polyhedral housing with a polygonal plane; a pin (180; 280) provided on one side of a corner of the housing to selectively protrude; a pin installation portion (150; 250) in which the pin (180; 280) is installed to be movable between a first position and a second position; a pin receiver (160; 260) provided on another side of the corner of the housing such that a pin of another module is to be inserted there into; and a magnet (140; 240) installed between the pin installation portion (150; 250) and the pin receiver (160; 260), and configured to apply magnetic force to both the pin (180; 280) provided in the pin installation portion (150; 250) and the pin (280; 180) of another module to be received in the pin receiver (160; 260), characterized in that the magnet of the first module is disposed such that, when a surface-to-surface coupling between the first module and the second module is cancelled, the magnitude of the magnetic force applied by the magnet of the first module to the pin of the first module becomes greater than the magnitude of the magnetic force applied by the magnet of the second module to the pin of the first module thereby causing the pin of the first module to move from the first position, in which the pin of the first module is protruding from the first module into the pin receiver, to the second position, in which the pin of the first module is received in the first module and the pin of the first module moves from the second position to the first position to be inserted into the pin receiver of the second module when the first module is surface-to-surface coupled to the second module. a polyhedral housing with a polygonal plane; a pin (180; 280) provided on one side of a corner of the housing to selectively protrude; a pin installation portion (150; 250) in which the pin (180; 280) is installed to be movable between a first position and a second position; a pin receiver (160; 260) provided on another side of the corner of the housing such that a pin of another module is to be inserted there into; and a magnet (140; 240) installed between the pin installation portion (150; 250) and the pin receiver (160; 260), and configured to apply magnetic force to both the pin (180; 280) provided in the pin installation portion (150; 250) and the pin (280; 180) of another module to be received in the pin receiver (160; 260), characterized in that the magnet of the first module is disposed such that, when a surface-to-surface coupling between the first module and the second module is cancelled, the magnitude of the magnetic force applied by the magnet of the first module to the pin of the first module becomes greater than the magnitude of the magnetic force applied by the magnet of the second module to the pin of the first module thereby causing the pin of the first module to move from the first position, in which the pin of the first module is protruding from the first module into the pin receiver, to the second position, in which the pin of the first module is received in the first module and the pin of the first module moves from the second position to the first position to be inserted into the pin receiver of the second module when the first module is surface-to-surface coupled to the second module.