Abstract: A roll-stamper for forming substrates of an information-recording medium includes at least one stamper being fastened along a peripheral face of a mirror roller, carrying on a surface thereof patterns each corresponding to a preformat for an information recording medium, also having stoppers fixed along both edges on the reverse side thereof, and being fastened to the mirror roller by inserting the stoppers respectively into negative stopping-grooves cut into the mirror roller in parallel with the axis of the mirror roller.

Abstract: Disclosed are a master holder of a stamper electroforming apparatus and an electroforming method using this master holder. The master holder is for use in a stamper electroforming apparatus that forms a metal film by electroforming on a conductive film formed on a master having a minute relief pattern on its surface; and this master includes: a contact ring for electrically connecting the conductive film to a power source; and a structure for controlling the rate at which the metal film is formed, which structure is provided on the contact ring and adapted to control the metal-film-formation rate such that the thickness of a peripheral portion of the metal film gradually decreases in the vicinity of the contact ring.

Abstract: A process for preparing a substrate sheet for optical recording mediums includes the steps of extruding a molten resin to form a resin sheet and bringing the resin sheet into pressure between a preformat roll and a roll disposed opposingly to said preformat roll to transfer a preformat pattern to the surface of the resin sheet, wherein the roll disposed opposingly to the preformat roll includes a roll whose surface is covered with an elastomeric resin.

Abstract: An encoder unit comprising an object to be detected having a track having a first region with a magnetization pattern at a predetermined pitch and a second region having no periodic magnetization pattern, and a detector having a magnetoresistance effect element arranged in the direction which intersects the direction of the magnetic flux of the magnetization pattern and in opposed relationship with the object to be detected. The encoder unit is simple in construction yet capable of detecting the position of the object to be detected with a higher degree of accuracy than conventional encoders.