A cutting insert comprising: a main body section elongated in a direction from a rear side to a front side; and a cutting section located in front of the main body section and comprising a top surface; a bottom surface; a first side surface located at the front side and between the top surface and the bottom surface; a second side surface located between the top surface and the bottom surface and adjacent to the first side surface; a front cutting edge disposed along a ridge line of the cutting section at an intersection between the top surface and the first side surface; a lateral cutting edge disposed along the ridge line at an intersection between the top surface and the second side surface, the lateral cutting edge having an ascending incline from the front cutting edge toward the main body section; and a rake face formed along the front cutting edge and the lateral cutting edge; wherein the lateral cutting edge comprises a first region near to the front cutting edge and a second region or a fourth region located to a rear of the first region; wherein the first region and the second region each having a linear shape in side view, and an angle of inclination of the second region with respect to the bottom surface being larger than an angle of inclination of the first region with respect to the bottom surface or wherein the first region has a linear shape and the fourth region has a curved shaped inclined with ascending as getting away from the front cutting edge in side view, and an angle of inclination of the fourth region is equivalent to an angle of inclination of the first region at an end portion located on the front side and the angle of inclination of the fourth region becomes larger from this end portion toward the rear side; and wherein the rake face is inclined with descending as getting away from the lateral cutting edge. a main body section elongated in a direction from a rear side to a front side; and a cutting section located in front of the main body section and comprising a top surface; a bottom surface; a first side surface located at the front side and between the top surface and the bottom surface; a second side surface located between the top surface and the bottom surface and adjacent to the first side surface; a front cutting edge disposed along a ridge line of the cutting section at an intersection between the top surface and the first side surface; a lateral cutting edge disposed along the ridge line at an intersection between the top surface and the second side surface, the lateral cutting edge having an ascending incline from the front cutting edge toward the main body section; and a rake face formed along the front cutting edge and the lateral cutting edge; wherein the lateral cutting edge comprises a first region near to the front cutting edge and a second region or a fourth region located to a rear of the first region; wherein the first region and the second region each having a linear shape in side view, and an angle of inclination of the second region with respect to the bottom surface being larger than an angle of inclination of the first region with respect to the bottom surface or wherein the first region has a linear shape and the fourth region has a curved shaped inclined with ascending as getting away from the front cutting edge in side view, and an angle of inclination of the fourth region is equivalent to an angle of inclination of the first region at an end portion located on the front side and the angle of inclination of the fourth region becomes larger from this end portion toward the rear side; and wherein the rake face is inclined with descending as getting away from the lateral cutting edge.