To provide a wire saw manufacturing silicon wafers with uniform thickness and to provide a cutting method using it.

This wire saw is provided with slack adjusting means 8 and 8 provided between a workpiece 7 and a pair of multi-grooved rollers 3d and 3d arranged across the workpiece 7 so as to freely advance/retreat respectively and adjusting slack of a wire row 4 by appropriately pushing the wire row 4 abutting on the workpiece 7. The wire row 4 is slackened by the slack adjusting means 8 and 8 in starting the cutting process by advancing/retreating the adjusting means 8 and 8, and the wire row 4 is continuously pushed by the slack adjusting means 8 and 8 in the latter stage of the cutting process, so that the cutting works are performed with the slack of the wire row 4 held as it is.