Tool body of cutting tool for indexable inserts, and round milling insert

A tool body onto which a round milling insert is mounted to configure a cutting tool for indexable inserts, wherein

• a mounting seat for mounting the round milling insert includes
• a seating surface coming into contact with one surface of the round milling insert,
• a female screw hole provided in the seating surface to receive a male screw for fixing the round milling insert, and
• a recessed portion provided so that only one of a plurality of protrusions is fitted thereto, the plurality of protrusions being formed in the round milling insert so as to protrude in a radial direction,
• the recessed portion has two opposed inner surfaces, each having a curved surface portion and a depth portion, the inner surfaces being disposed such that a distance between their respective curved surface portions gradually decreases toward their respective depth portions, at a contact area between the recessed portion and said protrusion fitted thereto out of the plurality of protrusions, and
• in the contact area, the inner surfaces respectively include ridge lines facing each other and protruding toward an internal space.