Cutting insert and indexable drill

A cutting insert comprising:

• an insert body;
• a post which is convexly formed at a lower side of the insert body and has a first central axis;
• a fastening surface which is formed at a lateral side of the insert body;
• a pressure receiving surface which is formed on the insert body in a direction orthogonal to the fastening surface;
• a tip cutting edge which is formed at a tip portion of the insert body and subjected to cutting processing;
• a lateral cutting edge which is formed at a lateral side of the insert body and subjected to cutting processing;
• and
• an insert flute which is formed at one side of the lateral cutting edge of the insert body and guides a discharge of cutting chips,
• wherein the fastening surface is provided as a surface of a cylindrical shape in which an upper radius and a lower radius are equal to each other, and a second central axis of the cylinder has a gradient with respect to the first central axis when viewed from a lateral side, and the second central axis is eccentric and has a gradient when viewed from a top side, and
• wherein the pressure receiving surface is formed to be inclined so that a portion, which is directed toward the tip cutting edge, is wider with respect to the first central axis when viewed from a lateral side of the cutting insert in a direction orthogonal to the pressure receiving surface.