A wire saw 10 is laid across sheaves 12, 14, 16, and 18 arranged within a substantially horizontal plane. The sheave 12 is rotated by a rotary motor 30 to horizontally drive the wire saw 10. Within a region formed by the wire saw laid across the sheaves, a stone material 80 is set on a carriage 82. The carriage 82 is provided with front wheels 83 and rear wheels 84, and the wheels are set on the pair of rails 85 laid so as to extend in a direction substantially orthogonal to a cutting portion 10A of the wire saw. When the carriage 82 is moved in the direction of the arrow F2 and the stone material 80 is brought into contact with the cutting portion from the inner side of the region formed by the wire saw, the wire saw smoothly bends within the same plane.