To provide a tool for cutting/machining capable of replacing a cutter by removing the cutter itself in a state of a screw mounted.

The cutter 32 mounted on a rotary shaft by a screw is constituted of a substantially circular-shaped principal part 33 and a projected part 34 having a cutting edge tip 35 extended in a radial direction from the principal part 33 and displaced in an axis direction. The cutter 32 is provided with a through hole having a substantially circular-shaped hole part 37 having a diameter larger than a head part of a screw arranged eccentrically in a radial direction from a center axis and another hole part 38 which is connected with the hole part 37, is arranged with the center axis as a center and has a diameter smaller than the head part of the screw. The smaller hole part 38 is surrounded by a countersink part arranged concentrically with the smaller hole part 38 since a step-like end edge is formed around the smaller hole part 38.