CUTTING INSERT AND MILLING TOOL

A cutting insert has a cutting edge member and a mounting portion. The mounting portion includes: a mounting surface on which the cutting edge member is mounted; a first side surface; and a second side surface. The mounting portion is provided with an introduction opening and a discharging opening of the coolant supplying passage. The first side surface is provided with a step constituted of a rising portion and a flat portion. In a cross section that is perpendicular to the rake face and that crosses each of the introduction opening and the discharging opening, a second distance is longer than a first distance and a value obtained by dividing the third distance by the fourth distance is more than or equal to 0.5 and less than or equal to 0.8 when it is assumed that the first distance represents a distance between the cutting edge and the mounting surface in a direction perpendicular to the rake face, the second distance represents a distance between the mounting surface and a boundary portion between the rising portion and the flat portion in the direction perpendicular to the rake face, the third distance represents a distance between the boundary portion and a tip of the cutting edge in a direction parallel to the rake face, and the fourth distance represents a distance between the second discharging opening portion and the tip of the cutting edge in the direction parallel to the rake face.