Abstract: A cutting tool including a cutting insert for which corner changing can be performed, the cutting tool having a large number of usable corners and thereby being cost effective, reducing cutting force during machining, and ensuring high rigidity. A negative-type cutting insert having a regular polygonal shape with five to eight corners is attached to an end of a tool holder such that one of two adjacent sides of an outer peripheral surface serves as a rake face having a negative rake angle, the other of the two adjacent sides serves as a front flank face, a ridge between the two adjacent sides of the outer peripheral surface serves as an end cutting edge, and a ridge between the side that serves as the rake face and one of top and bottom surfaces serves as a side cutting edge, and such that corner changing can be performed.