A throwaway insert enabling the use of a holder for a long period and having excellent chip evacuation is provided. The throwaway insert is formed in a substantially polygonal plate shape and includes a rake face formed on an upper surface thereof, a relief face formed on a side surface thereof, a main cutting edge formed along a ridge representing an intersection of the rake face and the relief face, which is divided into a plurality of main cutting edge divisions by at least one groove formed on the relief face, and a projection formed so as to protrude from the rake face in correspondence with each of the main cutting edge divisions.