A screw rotor lead correction calculation device includes an initial data input section configured to input an error as a distance with respect to a reference lead at each axial position of a rotor groove portion of a screw rotor, and a processing machine input correction amount/position output section configured to compute and output, based on the error as the distance input to the initial data input section, a lead correction amount with respect to the reference lead and a lead correction starting position as an axial position for starting lead correction. With this configuration, correction data for obtaining a screw rotor with a high-accuracy lead can be obtained from a lead error with respect to a reference lead in a screw rotor obtained by ground finish of the material of the screw rotor.