Motor drive system, motor controller, and motor

A motor drive system according to an embodiment of the present invention is provided with a motor having a strain area in which mechanical strain occurs due to excitation current, a motor controller for controlling driving of the motor, and a strain detection unit for detecting strain occurring in the strain area of the motor. The motor controller is provided with an estimation unit for estimating the speed and/or position of the motor on the basis of the strain in the strain area detected by the strain detection unit.