Abstract: A knapsack engine-driven tool driven by an engine provided on a knapsack frame consists of a supporting tool composed of a hollow tube made of a flexible rigid material, preferably of brass, whose base end is fixed onto the knapsack frame, in which the flexible rigid material can be held at a desired shape, a member for operating said engine provided on the edge portion of the hollow tube, a regulating wire which is inserted into the hollow tube for connecting said engine and said operating member, and a flexible protective member for covering said hollow tube. The knapsack engine-driven tool has a metal fixing member, preferably made of iron.