Cutting tool and indexable rotary cutting tool

A cutting insert comprising a first end surface, a second end surface arranged so as to be opposed to the first end surface, and a peripheral side surface extending between the first and second end surfaces, wherein:

• the first end surface and the second end surface each have, in a plan view, a shape comprised of one substantially quadrangular portion and two substantially semicircular portions which are respectively joined to two opposing sides of the substantially quadrangular portion;
• an intersecting edge between each of the first end surface and the second end surface and the peripheral side surface is provided with a cutting edge;
• the cutting edge is formed in at least part of the substantially semicircular portion;
• and
• a mounting hole is formed so as to penetrate substantially respective centers of the first end surface and the second end surface,
• wherein
• the cutting edge has a linear cutting edge formed in at least part of the substantially quadrangular portion and a circular-arc-shaped cutting edge formed in at least part of the substantially semicircular portion, the circular-arc-shaped cutting edge being connected to the linear cutting edge, and
• when defining a reference axis A which penetrates substantially respective centers of the first end surface and the second end surface, and a virtual plane C which extends in a direction perpendicular to the reference axis A and which is located at substantially respective centers of the first end surface and the second end surface,
• the cutting edge, in a side view, is raised so as to be apart from the virtual plane C, heading from the linear cutting edge to the circular-arc-shaped cutting edge, and is then lowered so as to be close to the virtual plane C, with an apex as a highest portion.