An indexable insert with a chip breaker configured such that chips produced under various cutting conditions from rough cutting to finish cutting can be disposed of in an optimum way. Protrusions are provided in a chip breaker groove to extend from a central land toward the respective corners of the insert. Each protrusion has a breaker wall which is concave and curved such that chips produced always collide against the breaker wall at an angle of 10 DEG -40 DEG so that the chips are curled helically with a helix angle of 10 DEG -40 DEG and broken into small pieces reliably.
