PURPOSE: To surely prevent a cutting liquid from leaking by means of an inexpensive device by inserting a bag body formed of an elastic material into a rear end opening part in a pipe material and injecting the fluid to the inside of the bag body so as to seal the whole lower face or the whole inner circumference face.

CONSTITUTION: A cutting liquid leakage preventing device 1 is provided with an endless bag body 3 formed of an elastic material such as rubber, and both double-folded ends of the bag body 3 are airtightly installed on a supporting plate 5 via a pressing plate 7 by means of fastening by a fastening member 9. In use, when a pipe material 13 is cut by means of a band saw machine, a circular saw machine, or the like while cutting liquid injected to a saw blade, the bag body 3 is inserted into the inside of the pipe material 13 from its rear end opening end, and then, fluid is injected from a fluid injection port 11 arranged in one end of the bag body 3 so as to expand the bag body 3. In this way, most of the inner circumference face of the pipe material 13 is sealed by means of the outer circumference face of the bag body 3, so that cutting liquid fed in cutting of the pipe material 13 is prevented from leaking to the rear end side of the pipe material 13.