To provide a technique which makes a wire saw cutting device having size and capacity equivalent to those of a land-type device enough capable of carrying out the underwater grinding/cutting work of a concrete structure by eminently reducing the rotational resistance in water of a driving pulley.

Both sides of the driving pulley are blocked with doughnut-shaped disks, and a closed space is formed inside. The driving pulley is driven by a hydraulic motor, and pinions moving the driving pulley and a driving motor are rotated/driven by a torque converter. By blocking both sides of the pulley, the surface area of a part which contacts water and receives the resistance of water can eminently be reduced to reduce the rotational resistance. The closed space of the driving pulley produces buoyancy in water so that the weight in water of the driving pulley can be reduced. Accordingly, driving force necessary for rotation can be saved by a weight reduction under the buoyancy.