A cutting insert comprising: a cutting edge member; and a mounting portion on which the cutting edge member is mounted, wherein the cutting edge member includes a rake face and a flank face continuous to the rake face, and a ridgeline between the rake face and the flank face constitutes a cutting edge, the mounting portion includes a mounting surface on which the cutting edge member is mounted, a first side surface continuous to the mounting surface, and a second side surface opposite to the first side surface, the mounting portion is provided with a coolant supplying passage that opens in each of the first side surface and the second side surface, an opening of the coolant supplying passage in the first side surface constitutes a discharging opening of the coolant supplying passage, an opening of the coolant supplying passage in the second side surface constitutes an introduction opening of the coolant supplying passage, the first side surface is provided with a step constituted of a rising portion and a flat portion continuous to the rising portion, and when it is assumed that a first cross section represents a cross section that is perpendicular to the rake face and that crosses each of the introduction opening and the discharging opening, the discharging opening has a first discharging opening portion and a second discharging opening portion in the first cross section, the second discharging opening portion being located between the first discharging opening portion and a straight line extending along the mounting surface, characterized in that: a second distance is longer than a first distance and a value obtained by dividing a third distance by a 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. a cutting edge member; and a mounting portion on which the cutting edge member is mounted, wherein the cutting edge member includes a rake face and a flank face continuous to the rake face, and a ridgeline between the rake face and the flank face constitutes a cutting edge, the mounting portion includes a mounting surface on which the cutting edge member is mounted, a first side surface continuous to the mounting surface, and a second side surface opposite to the first side surface, the mounting portion is provided with a coolant supplying passage that opens in each of the first side surface and the second side surface, an opening of the coolant supplying passage in the first side surface constitutes a discharging opening of the coolant supplying passage, an opening of the coolant supplying passage in the second side surface constitutes an introduction opening of the coolant supplying passage, the first side surface is provided with a step constituted of a rising portion and a flat portion continuous to the rising portion, and when it is assumed that a first cross section represents a cross section that is perpendicular to the rake face and that crosses each of the introduction opening and the discharging opening, the discharging opening has a first discharging opening portion and a second discharging opening portion in the first cross section, the second discharging opening portion being located between the first discharging opening portion and a straight line extending along the mounting surface,