Provided is a module assembly including a plurality of modules. The modules each include a polyhedral housing with a polygonal plane, a pin provided on one side of a corner of the housing to selectively protrude, a pin installation portion in which the pin is installed to be movable, a pin receiver provided on another side of the corner of the housing such that a pin of another module is to be inserted thereinto, and a magnet installed between the pin installation portion and the pin receiver, and configured to apply magnetic force to both the pin provided in the pin installation portion and the pin of the other module to be received in the pin receiver.