A rotation controller for an AC electric motor includes a space vector generator, a current change ratio obtainer, and a rotational angle calculator. The space vector generator generates at least a first magnetic field in a first direction and a second magnetic field in a second direction crossing the first direction in a rotation plane of a saliency-exhibiting rotor. The space vector generator synthesizes the first magnetic field and the second magnetic field into a synthesized magnetic field. The current change ratio obtainer acquires a first current change ratio of a first current generated in the first direction in a stator and a second current change ratio of a second current generated in the second direction in the stator. The rotational angle calculator calculates a rotational angle of the saliency-exhibiting rotor based on at least the first and second current change ratios and the first and second directions.