To perform cutting work of a wire saw without causing fluctuation in working load even if a cutting length varies with cutting work for a work.

A wire 15 is wound at a preset pitch between working rollers 13, 14. Slurry is supplied onto the wire 15 while the wire 15 is running, and a work 21 is put in contact with the wire 15 to perform cutting work for time work 21. In cutting work for the work 21, working load is detected by a working load detector 44. In accordance with a result, detected by the detector 44, a controller 38 controls the running speed of the wire 15 and the supply amount of the slurry to keep working load per unit cutting length of the work 21 constant.