To enable simple, safe and sure laser peening work even when mechanical components or steel structures under or after construction are worked on the site, since no preparation is needed such as immersing a workpiece in water or coating it and time and labor are not required for installation of equipment.

The apparatus for performing laser peening is equipped with a handy performance cylinder 1 including: a cylindrical body section 2 incorporating an optical fiber 4 for transmitting a laser beam 10, a hose 5 for making a transparent liquid 11 flow through, and a lens 6 for condensing a laser beam passing through the optical fiber; and a cylindrical head section 3 which is connected to the tip of the cylindrical body section 2 to surround an interval space between the lens and a workpiece, which has the enclosure filled with the transparent liquid passing the hose, and which is the propagation medium of the laser beam passing through the optical fiber.