To provide a cover fitted with a grooved roller of a wire saw capable of easily performing maintenance work and capable of preventing the scattering of a slurry at the time of trial operation.

A pair of guide rails 44, 44 are arranged to the outer peripheries of both end parts of grooved rollers 18A-18C and a freely extensible cover 54 is provided to a pair of the guide rails 44, 44 in a freely slidable manner. When maintenance work is performed, the grooved rollers 18A-18C are opened forwardly by the cover 54. By this constitution, the tensioning work of wire rows 20 can be easily performed without obstructing work. At a time of trial operation, the cover 54 covers the front parts of the grooved rollers 18A-18C. By this constitution, the scattering of a slurry to the periphery can be prevented.