A laser peening processing device comprising: a laser oscillator for emitting laser light; a nozzle for condensing and irradiating the laser light toward a surface to be processed of a workpiece, with injecting liquid toward the surface to be processed, an irradiation direction of the laser light being vertically downward, an injection direction of the liquid being vertically downward; a liquid supply system for supplying the liquid to the nozzle; an inclining structure being composed of a robot arm and a controlling device, the inclining structure being configured to incline the workpiece to make the injection direction of the liquid be different from a normal direction of the surface to be processed, 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 being flowed in a direction depending on an inclined direction of the surface to the injection direction of the liquid, the robot arm being configured to hold the workpiece or a jig for attaching the workpiece, the robot arm being configured to variably control an inclined angle of the surface to be processed to the injection direction of the liquid; and a moving structure for moving the nozzle relatively to the workpiece, the controlling device being configured to control the moving structure and the robot arm to perform a parallel translation of the nozzle by the moving structure in conjunction with a rotation movement of the workpiece by the robot arm, the moving structure and the robot arm being controlled so that the laser light is focused on the surface to be processed, and wherein the controlling device is configured to incline the workpiece with the robot arm to make the inclined angle of the surface to be processed to the injection direction of the liquid become constant or within a predetermined range, during the parallel translation of the nozzle, based on three-dimensional information showing a shape of the surface to be processed. a laser oscillator for emitting laser light; a nozzle for condensing and irradiating the laser light toward a surface to be processed of a workpiece, with injecting liquid toward the surface to be processed, an irradiation direction of the laser light being vertically downward, an injection direction of the liquid being vertically downward; an inclining structure being composed of a robot arm and a controlling device, the inclining structure being configured to incline the workpiece to make the injection direction of the liquid be different from a normal direction of the surface to be processed, 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 being flowed in a direction depending on an inclined direction of the surface to the injection direction of the liquid, the robot arm being configured to hold the workpiece or a jig for attaching the workpiece, the robot arm being configured to variably control an inclined angle of the surface to be processed to the injection direction of the liquid; and a moving structure for moving the nozzle relatively to the workpiece, the controlling device being configured to control the moving structure and the robot arm to perform a parallel translation of the nozzle by the moving structure in conjunction with a rotation movement of the workpiece by the robot arm, the moving structure and the robot arm being controlled so that the laser light is focused on the surface to be processed, and wherein the controlling device is configured to incline the workpiece with the robot arm to make the inclined angle of the surface to be processed to the injection direction of the liquid become constant or within a predetermined range, during the parallel translation of the nozzle, based on three-dimensional information showing a shape of the surface to be processed.