A method of assembling a rotor including a cylindrical rotor core and a permanent magnet that is held in a hole portion provided in the rotor core such that a longitudinal direction of the permanent magnet is parallel to an axis of the rotor core. The method includes: a load measuring step of measuring a load applied to the permanent magnet or/and the rotor core when the permanent magnet is brought into contact with the rotor core; and a moving step of moving the permanent magnet or/and the rotor core so as to change a position of the permanent magnet relative to the rotor core, depending on data relating to the load measured at the load measuring step, such that a positional deviation between the permanent magnet and the hole portion is reduced. Also disclosed is a control device for a rotor assembly apparatus.