The present invention provides a pipe straightener, which consists of three roller wheel units and a restraining sleeve, wherein each of the roller wheel units is juxtaposed, and the roller wheel units enclose and are configured to form a long straight-formed passageway. The passageway is used to enable metal pipes to pass therethrough. The restraining sleeve encloses and covers each of the roller wheel units, thereby restraining each of the roller wheel units. Each of the roller wheel units is mainly structured from a wheel carrier and a plurality of roller wheels. One side of the wheel carrier is a first side, and the other side is a second side. The first side is adjacent to the passageway, and the second side is adjacent to the restraining sleeve.