CUTTING INSERT AND GEAR CUTTER

A cutting insert which is excellent both in manufacturing performances and dimensional precision and forms a pair with a tool body and a gear cutter including the cutting insert are provided. A cutting insert has a first face which is a rake face, a second face, a peripheral side face, and a mounting hole. On a ridge line where the first face and the peripheral side face cross each other, a cutting blade is formed. The cutting blade includes a corner part capable of machining a tooth bottom of a gear, and a main part extending to the corner part. The peripheral side face includes an inner side face in contact with a tool body and a first flank facing the main part. The mounting hole penetrates the first flank and the inner side face so that a center axis crosses the inner side face perpendicularly. The cutting insert is formed having a wedge shape such that thickness of the first flank and the inner side face becomes smaller as it goes from one end to the other end.