To provide a spiral groove machining apparatus for a large cylindrical work which can achieve the grooving with high accuracy while keeping the constant groove depth of a spiral groove to be machined.

This spiral groove machining apparatus for the large cylindrical work 1 comprises a grinding wheel 21 to machine the spiral groove while relatively moving along the spiral groove of the large cylindrical work 1, a guide pad 21 which is held adjacent to the grinding wheel 21 and relatively moved along the spiral groove together with the grinding wheel 21 while keeping the constant protrusion in the spiral groove of the grinding wheel 21 in an abutted manner on a top surface of a ridge part adjacent to the spiral groove while the grinding wheel 21 machines the spiral groove, a grinding wheel pressing means 24 to elastically press the grinding wheel 21 against the spiral groove by the preset pressure, and a guide pad holding means 19 to hold the guide pad 22 in an adjustable manner of the holding position so that the protrusion from the guide pad 22 of the grinding wheel 21 reaches the preset protrusion.