To provide a cutting insert, a cutting tool, and a cutting method capable of stably cutting over a long period by suppressing the elastic deformation or wear of the contact portion of a tool holder on the cutting insert.

This cutting tool comprises a cutting insert having an insert body with an upper surface and side surfaces and edge parts formed between the upper surface and the side surfaces, and a tool holder having an insert mounting part to which the cutting insert is attached. The cutting insert comprises a member having a hardness lower than that of the insert body installed on a part of the surface thereof. The cutting insert is brought into contact with the insert mounting part at the low hardness member.