PURPOSE: A light guide plate manufacturing device is provided to be perfectly adhered to a mask while a light guide plate is transferred and to steadily process a pattern. CONSTITUTION: A mask(3) in which a pattern hole is formed is adhered to the upper surface of a light guide plate(2) which is transferred through a feeding unit(1). A processing source is radiated on the pattern hole and a pattern is formed on the light guide plate. The mask is closed to the upper surface of the light guide plate or is separated from the upper surface of the light guide plate. A magnetic force unit having magnetic force is ascended and descended to the bottom surface of the light guide plate. The mask and the magnetic force unit are transferred to a transferring direction of the light guide plate at the same time at the top and bottom surface of the light guide plate.