PURPOSE: To simply and surely fix a ring and to strengthen upper end edge of inner face in a cylinder bore by irradiating laser beam toward butting boundary face between annular stepping face in the cylinder bore and annular lower end face in the ring and welding both faces.

CONSTITUTION: The ring 19 is fitted into the annular stepping part 15 in the cylinder bore 12, and after abutting the annular lower end face 20 in the ring 19 on the annular stepping face 16, welding wire 21 is supplied to a groove 22 at between inner circumferential end edges of both faces 16, 20 and positioned. Successively, the laser beam 24 irradiates on the butting face with the abutted annular stepping face 16 and the annular lower end face 20 in the ring 19 from a welding torch 23 at outer part of the bore 12. Both faces 16, 20 and the welding wire 21 are solidified after melting and mixing, and the annular lower end face 20 in the ring 19 is stuck to the annular stepping face 16 in the cylinder bore 12. Under the above point, the annular lower face 21 in the ring 19 and the annular stepping face 16 in the cylinder bore 12 are welded over the whole faces.