To provide a tool for blocking a pipe, with which a part of a circular pipe can be blocked accurately.

A tool for blocking a pipe is a pinch-off tool 2 and includes a body on a part of which a notch 6 is provided and a movable part 8 which is made movable relatively to the body inside the notch 6 and on which a projecting part 4 projected toward a first side face 6a inside the notch 6 is provided. The pinch-off tool 2 blocks a part of a copper pipe 20 arranged inside the notch 6 by crushing a part of the copper pipe by means of the distal end of the projecting part 4 by moving the movable part 8. The projecting part 4 has a trapezoidal shape in the cross section along the pipe axis of the copper pipe 20 and extends in a direction orthogonal to the direction of the pipe axis, also a curvature is provided on boundaries between the top face 4a and the slopes 4b of the projecting part 4, and in the top face 4a, there is provided a recessed part 4c which comprises a groove along the direction of the pipe axis, the groove width of the groove being shorter than the diameter of the copper pipe 20.