The present invention relates to a method of controlling an induction motor (1) with a rotational speed-control apparatus (2-16), which includes a power-conversion unit (2), for such controlling a frequency and current output from said power-conversion unit in accordance with a rotational speed instruction value (ωr*) that if said rotational speed instruction value is less than a predetermined value, current output from said power-conversion unit is controlled at a predetermined value larger than that in an ordinary no-load operation, and the value of said current is corrected corresponding to a value which is obtained by adding an estimated slip frequency value (ωs^) calculated based on the value of said voltage output from said power-conversion unit to a calculated slip frequency value (ωs*) calculated by using a value of current output from said power-conversion unit.