Provided is there a piece with a magnet for building a toy, and more particularly to a piece with a magnet for building a toy, the piece having at least two or more end and a magnet case having a magnet with south and north pole faces inside, rotatably provided on each end, capable of connecting to the other piece of the same construction, without sliding with respect to each other, by automatically enabling the north or south pole face of the one magnet to be opposite to the south or north pole face of the other magnet.