PURPOSE: To provide the working method of a cylindrical inner surface by which a groove can be formed with a high dimensional accuracy on the inner surface of a cylinder having a small diameter.

CONSTITUTION: A laser beam α is converged by a condensing lens 4, reflected by a small reflection mirror 5 provided inside a bearing sleeve 1, and converged on the inner circumferential surface 1a of the bearing sleeve 1. By moving and rotating the bearing sleeve 1 in the Z and θ directions respectively, a focal point S is moved on the inner circumferential surface 1a of the bearing sleeve 1, and grooves 2 are formed on the inner surface of the bearing sleeve 1.