Abstract: According to one implementation, a laser peening processing device includes a laser peening processing device includes a laser oscillator, a nozzle and an inclining structure. The laser oscillator emits laser light. The nozzle condenses and irradiates the laser light toward a surface to be processed of a workpiece, with injecting liquid toward the surface to be processed. The inclining structure inclines at least one of the nozzle and the workpiece to make an injection direction of the liquid be different from a normal direction of the surface to be processed. The air bubbles arising by at least one of collision between the liquid and the surface to be processed and shock by irradiation of the laser light on the surface to be processed are flowed in a direction depending on an inclined direction of the surface to the injection direction of the liquid.