A cutting insert comprising: a first surface ; a second surface located opposite to the first surface; and a side surface continuous with both the first surface and the second surface, wherein a ridge line between the first surface and the side surface includes a cutting edge , the first surface has a rake surface continuous with the cutting edge, and a reference surface located on a side opposite to the cutting edge with respect to the rake surface and having a planar shape, the cutting edge has a corner cutting edge , a flat drag continuous with a first end portion (C1) of the corner cutting edge, and a main cutting edge continuous with a second end portion (C2) of the corner cutting edge, the second end portion being located opposite to the first end portion, the rake surface has a first rake surface portion continuous with the flat drag, a second rake surface portion continuous with the main cutting edge, and a third rake surface portion continuous with the corner cutting edge and located between the first rake surface portion and the second rake surface portion, the first rake surface portion has a first inclined surface inclined at a first angle (θ1) with respect to the reference surface, the second rake surface portion has a second inclined surface inclined at a second angle (θ2) greater than the first angle with respect to the reference surface, the first angle and the second angle are positive angles with respect to the reference surface, the first end portion and the second end portion are higher than the reference surface in a direction perpendicular to the reference surface, and a first step portion rising from the third rake surface portion and continuous with the first rake surface portion is provided on the rake surface, characterised in that , the main cutting edge extends so as to intersect the reference surface when viewed in a direction parallel to the reference surface. a first surface ; a second surface located opposite to the first surface; and a side surface continuous with both the first surface and the second surface, wherein a ridge line between the first surface and the side surface includes a cutting edge , the first surface has a rake surface continuous with the cutting edge, and a reference surface located on a side opposite to the cutting edge with respect to the rake surface and having a planar shape, the cutting edge has a corner cutting edge , a flat drag continuous with a first end portion (C1) of the corner cutting edge, and a main cutting edge continuous with a second end portion (C2) of the corner cutting edge, the second end portion being located opposite to the first end portion, the rake surface has a first rake surface portion continuous with the flat drag, a second rake surface portion continuous with the main cutting edge, and a third rake surface portion continuous with the corner cutting edge and located between the first rake surface portion and the second rake surface portion, the first rake surface portion has a first inclined surface inclined at a first angle (θ1) with respect to the reference surface, the second rake surface portion has a second inclined surface inclined at a second angle (θ2) greater than the first angle with respect to the reference surface, the first angle and the second angle are positive angles with respect to the reference surface, the first end portion and the second end portion are higher than the reference surface in a direction perpendicular to the reference surface, and a first step portion rising from the third rake surface portion and continuous with the first rake surface portion is provided on the rake surface, characterised in that , the main cutting edge extends so as to intersect the reference surface when viewed in a direction parallel to the reference surface. <EOS>