A mixing rotor includes: a rotor shaft portion that includes a cooling passageway formed therein, and a mixing blade portion that is formed in an outer circumferential portion of the rotor shaft portion, wherein each of the long blades of the mixing blade portion includes a land portion as an end surface of the long blade facing a radially outside of the mixing rotor, a length of each of the long blades in the axis direction is set to be 0.6 times or more as large as a length of the mixing blade portion in the axis direction, a biting angle of each of the long blades is set to an angle equal to or smaller than 31°, and a center angle with respect to a land width as a width of the land portion in the cross-section of each of the long blades orthogonal to the axis direction is set to an angle equal to or larger than 7°.