Cutting insert and indexable cutting tool

A cutting insert comprising:

• an insert body having a polygonal plate shape;
• a pair of polygonal planar first surfaces;
• a through hole which penetrates the insert body, opens to the pair of the first surfaces and extends in a direction of a first axis;
• a second surface which is disposed on a circumferential surface of the insert body which connects the pair of first surfaces to each other, and faces a direction of a second axis orthogonal to the direction of the first axis;
• a third surface which is disposed on the circumferential surface, is connected to the pair of the first surfaces and the second surface and faces a direction of a third axis orthogonal to the direction of the first axis and different from the direction of the second axis;
• and
• cutting edges having a portion located at an intersection ridge line between the first surface and the second surface and a portion located at an intersection ridge line between the second surface and the third surface,
• wherein the second surface has a projection part protruding in the direction of the second axis from the second surface, and
• as viewed from the direction of the second axis, the through hole and the projection part are disposed to overlap each other.