A system for manufacturing an assembly board includes an undersupporting device, a carrier configured to hold the undersupporting device, a transporter, an undersupporting-device installer attachable to and detachable from the undersupporting device, a board processor, and a magnet provided on a lower surface of the undersupporting device. The transporter transports the undersupporting device to a working position by transporting the carrier to the working position while the carrier holds the undersupporting device on the lower surface of the carrier. The transported undersupporting device is fixed to the undersupporting-device installer by a magnetic force of the magnet at the working position. The transporter transports the board to the working position. The undersupporting device supports the lower surface of the board when the board is transported to the working position. The board processor performs a predetermined processing to an upper surface of the board.