PURPOSE: To provide a simple and fast making or low convex or concave pattern by a method wherein some small iron steel pieces are projected continuously or intermittently by a centrifugal projecting device onto a surface of the natural stone.

CONSTITUTION: Stone material 1 to be worked is transported by a belt conveyor 3. Small pieces of iron steel 4 are projected from the projection machine 5 onto a surface of the stone material to be worked, and then a pattern is formed on a surface of the stone material by the shock force of the small iron steel pieces. Small pieces of iron steel 4 projected onto the stone material are recovered and used again in a repetitive manner. Some fine dusts generated from the stone material are separated from the small pieces and removed by a proper process. The stone material may be transported by a rotary table other than a belt conveyor.