An indexable milling insert having triangular shape, the cutting insert comprising a mounting hole placed centrally in the cutting insert, a first support surface and a second support surface, which support surfaces are parallel with each other and act as alternating support surfaces, that the cutting insert comprises three equally long sides, which extend between the parallel support surfaces, that the cutting insert is provided with main cutting edges, which are orientated perpendicularly to the center axis of the mounting hole as well as provided in such a way that a rotation of the cutting insert around the center of the mounting hole to an alternative insert seat alternatively a turning of the cutting insert to an alternative insert seat provides an identical location of the main cutting edges in relation to a piece to be machined, and that the wedge angles (β) of the cutting insert are in the range of 70°≦β≦85°. The invention also relates to a milling tool equipped with the milling inserts defined above. The cutting insert comprises planar support surfaces situated on the sides, and the support surfaces in the respective sides form mutual angles of 60°.