A process for preparing a magnet roller comprising a plurality of bar-like magnet pieces in a high working efficiency and in an improved adhesion accuracy, which comprises the steps of regulating the bonding position of at least two magnet pieces by their outer peripheral surfaces and their end surfaces, applying an adhesive from the inner surface side of the magnet pieces to the adhesion faces of the magnet pieces for bonding one magnet piece to another magnet piece to form a magnet block, and bonding and fixing the magnet block to a shaft. At least one of the adhesion faces which are in contact with each other may have a plurality of grooves to facilitate penetration of the adhesive into the interface of adjacent two magnet pieces.