Cutting insert, tool body, and edge-replaceable rotary cutting tool

A cutting insert of a positive type that is attached to a tool body rotating around a rotation axis and that has a polygonal plate shape rotationally symmetrical with respect to a center line extending in a thickness direction, the cutting insert comprising:

• a rake surface that constitutes one of a pair of polygonal surfaces;
• a seating surface that constitutes the other of the pair of polygonal surfaces;
• a side surface that connects the rake surface and the seating surface;
• a cutting edge portion that is formed at an intersecting ridge between the rake surface and the side surface and that includes a main cutting edge located at a side part of the rake surface, a sub-cutting edge connected to one end side of the main cutting edge, and a corner edge connected to an end part of the sub-cutting edge on an opposite side to a main cutting edge side and located at a corner part of the rake surface;
• and
• an attachment hole that penetrates the cutting insert in the thickness direction and that is used for attaching the cutting insert to the tool body,
• wherein the rake surface is formed with a first plane parallel to the seating surface,
• an outer periphery of the first plane includes a plurality of curved portions having different radii of curvature, and the outer periphery of the first plane in the vicinity of the corner part is formed to project toward the side surface of the cutting insert in the vicinity of the corner part,
• on the rake surface, a breaker including a first inclined surface and a second inclined surface is provided between the cutting edge portion and the first plane around an entire circumference of the cutting insert, and
• when a distance from the seating surface to a tip of the cutting edge portion in the thickness direction is denoted by L11, a distance from the seating surface to the first plane in the thickness direction is denoted by L12, and a distance from the seating surface to a deepest portion of the breaker in the thickness direction is denoted by L13, a relationship of L11>L12>L13 is satisfied over an entire circumference of the cutting edge portion.