Abstract: Laser peening (LP) is a process to introduce residual compressive stress on metal surface by irradiating laser pulses underwater without any surface preparations. Toshiba has developed and applied LP system to preventive maintenance against stress corrosion cracking (SCC) in nuclear power reactors since 1999. The system is composed of laser oscillators, a beam delivery system, a laser irradiation head, remote handling equipment and a monitor/control system. In the early applications, a rigidly laser beam delivery system with many mirrors and beam gui de pipes was accomplished. A flexible fiber-delivery system has been developed for accessing to the narrow place, and presently it is adopted mainly. As these beam-delivery systems require a wide installation space and difficult operation, a simple and small system is desired. In or der to meet this demand, we are developing the small-sized next generation LP system that builds in the laser oscillator inside the remote handling equipment. In the next generation system new irradiating method is adopted, stress improvement speed is faster than the present system.