Cutting insert and replaceable-edge rotary cutting tool

An indexable rotary cutting tool comprising:

• a cutting insert having a polygonal plate shape;
• and
• a holder in which the cutting insert is attachably and detachably mounted and that is configured to rotate about a rotation axis,
• wherein the cutting insert includes a rake face configured to form one of a pair of polygonal surfaces, a seating surface configured to form the other of the pair of polygonal surfaces, a side surface configured to connect the rake face and the seating surface, and a mounting hole configured to be open to the rake face and the seating surface and to penetrate the cutting insert in a thickness direction,
• a cutting edge portion is provided on an intersecting ridgeline between the rake face and the side surface,
• the cutting edge portion includes a corner edge and a main cutting edge connected to the corner edge,
• the main cutting edge is linear in both of a plan view in which the rake face is viewed as a front and a side view in which the side surface is viewed as a front,
• the corner edge includes a first arc edge connected to the main cutting edge and an outermost peripheral arc edge located at an outermost peripheral portion in the corner edge,
• the first arc edge and the outermost peripheral arc edge are arc-shaped cutting edges having different radii of curvature in a tool rotation trajectory, and
• the holder includes an insert mounting seat that comes into contact with a flank face for the wiper edge of the cutting insert and the seating surface.