To provide a pipe cutting guide by a power tool, a support for a pipe to be cut, and a method of cutting the pipe using the power tool and the support, wherein a rigid vinyl pipe with a large diameter is cut by a grinder in a simple, correct and safety manner.

The pipe cutting guide consists of a tube holding guide ring (1), a guide adapter (2) to be mounted along the circumferential direction of the ring, a lock nut (3) with a free-wheeling attachment to be mounted on a coupling member (5) of the guide adapter, and the grinder (4) with a driving shaft (10) with the lock nut mounted, or the like. The guide ring (1) has a split base end hinged, and a stopper (7) is provided at a split tip. In addition, the guide adapter (2) is equipped with a recessed groove (8) to be fitted with the guide ring (1), and the base (9) of the ring is formed to be arcuate to conform to the outer diameter surface of a tube. Further, a bearing (11) which does not transmit the driving force of the driving shaft (10) to the coupling member (5) is built into an attachment (6) on the side of the lock nut (3).