Four single-cell cavities are used for beam acceleration in the Photon Factory storage ring. An RF power was supplied by two 180-kW klystrons until July, 1988. The maximum stored current of the ring was 370 mA, limited by the available RF-power. In order to store more high-current beams, the RF-power source was reinforced by an addition of two klystrons in 1988. Hence, each cavity is driven by a single klystron. Related devices such as a high-voltage power supply for the klystron, a circulator, waveguides and low-level RF circuits were newly installed. The reinforcement allowed us to achieve a stored current of 500 mA at 2.5 GeV. (author).