To manufacture a magnet piece for magnet roller from which desired magnetic force patterns are readily obtained and which is low-cost and flexible.

By pouring a composite resin magnet material made from ferrite particles and polymeric materials into a mold cavity 1 of a metal mold 10, this device and method for manufacturing the magnet piece for magnet roller make a magnetic field act to the composite resin magnet material in the mold cavity 1 to form the magnet piece, using yokes 21, 22 for applying magnetic field facing the mold cavity. Further, in the device and the method for manufacturing the magnet piece for magnet roller, the metal molds 11, 12 formed with the mold cavity 1 and the yokes for applying magnetic field are constituted by another member such that the relative position between them is changeable.