To surely and efficiently cut a plastic bottle with the tool having a simple structure by providing the inner surface of a cylindrical cover body of the tool with a blade so that the blade projects from the inner surface and holding the blade with a blade holder placed in the cover body.

In this tool, a cover body 1 is made of a plastic material such as ABS(acrylonitrile-butadiene-styrene) resin and formed into a cylindrical shape so that the cover body 1 can be engaged with the side surface of a PET (polyethylene terephthalate) bottle or the like while making a little allowance between them. The cover body 1 is fitted on its outside with a plastic bar-like grip 2, adjacently to the upper end surface 1a of the body 1 and obliquely to the side surface of the body 1. This grip 2 is hollow and provided with a long and narrow open hole 7 formed in the central part of a surface facing downward of the grip 2 and in the longitudinal direction of the grip 2 and also, this open hole 7 is fitted with a screw member 8. The cover body 1 is also provided with an opening connected to the hollow part of the grip 2 and a long and narrow thin-sheetlike blade 3 is inserted into the hollow part of the grip 2 from this opening and the blade 3 is fastened with the screw member 8.