The present invention provides a method of cutting a workpiece efficiently with high accuracy by utilizing tension adjusters to approximate tension in a wire in a wire saw to a predetermined target tension while effectively reducing only tension in a winder-side wire. The method comprises a forward-driven cutting step of cutting a workpiece while moving a wire forward, a first switching step of reversing a driving direction of the wire, a backward-driven cutting step of cutting the workpiece while moving the wire backward, and a second switching step of reversing a driving direction of the wire and returning to the forward-driven cutting step, the steps being repeated in this order. In both switching steps, only tension in a winder-side wire is reduced by tension manipulators. A reduction in target wire tension therefor is performed after completion of deceleration of the wire in each switching step.