Accurate controls for the speed and the torque of induction motors (IM) are realized using the detected secondary current (I/sub 2/) signal with the inverter having a constant ratio of the primary voltage over the driving frequency (V/sub 1//f). A new method for detecting I/sub 2/ is presented setting a MI sensor head inside a drilled hole through a shaft of an actuator type IM, in which an almost pure I/sub 2/ signal having the slip frequency is stably detected, An accurate and reliable control system for the IM is constructed using the I/sub 2/ feedback loop with the inverter.