A cutting tool comprising: a holder having a first surface and a second surface provided to be separated from each other to sandwich an axis line; a head including a cutting edge portion located between the first surface and the second surface, and a shank portion configured to hold the cutting edge portion; and a fastening portion configured to fix the head to the holder, the holder being provided with a first hole and a second hole, the first hole extending in a first direction and a third direction, the first direction being inclined by a first angle (Θ1) toward the cutting edge portion relative to a direction perpendicular to the axis line, the third direction being inclined by a second angle (Θ2) relative to a second direction extending from the second surface toward the first surface when viewed in a direction parallel to the axis line, the second hole communicating with the first hole, the second hole extending in the direction parallel to the axis line, the shank portion having a flat surface portion, the shank portion being provided inside the second hole, the fastening portion being provided inside the first hole, the fastening portion being in contact with the flat surface portion, in a plane perpendicular to the axis line, a third angle (Θ3) between the second direction and a fourth direction perpendicular to the flat surface portion being larger than the second angle (Θ2), the third angle being less than 90°, characterized in that when viewed in the direction parallel to the flat surface portion and perpendicular to the axis line, the flat surface portion is inclined relative to the axis line by an angle being substantially the same as the first angle (Θ1), and wherein the shank portion has a contact portion opposite to the flat surface portion, and is provided with a swaging prevention groove located between the flat surface portion and the contact portion. a holder having a first surface and a second surface provided to be separated from each other to sandwich an axis line; a head including a cutting edge portion located between the first surface and the second surface, and a shank portion configured to hold the cutting edge portion; and a fastening portion configured to fix the head to the holder, the holder being provided with a first hole and a second hole, the first hole extending in a first direction and a third direction, the first direction being inclined by a first angle (Θ1) toward the cutting edge portion relative to a direction perpendicular to the axis line, the third direction being inclined by a second angle (Θ2) relative to a second direction extending from the second surface toward the first surface when viewed in a direction parallel to the axis line, the second hole communicating with the first hole, the second hole extending in the direction parallel to the axis line, the shank portion having a flat surface portion, the shank portion being provided inside the second hole, the fastening portion being provided inside the first hole, the fastening portion being in contact with the flat surface portion, in a plane perpendicular to the axis line, a third angle (Θ3) between the second direction and a fourth direction perpendicular to the flat surface portion being larger than the second angle (Θ2), the third angle being less than 90°, characterized in that when viewed in the direction parallel to the flat surface portion and perpendicular to the axis line, the flat surface portion is inclined relative to the axis line by an angle being substantially the same as the first angle (Θ1), and wherein the shank portion has a contact portion opposite to the flat surface portion, and is provided with a swaging prevention groove located between the flat surface portion and the contact portion.