A strain sensing apparatus includes a pair of magnetic layers disposed on a shaft to which an external force is applied to cause strain in it. The magnetic layers have magnetic permeabilities which change in opposite directions in response to the strain in the shaft. A sensing coil is disposed to face the magnetic layers with a spacing disposed between the coil and the magnetic layers. An exciting AC voltage is applied across the sensing coil. A change in self-inductance of the coil caused by the permeability changes of the magnetic layers due to the shaft strain is derived as an electrical signal representative of the magnitude of the shaft strain.
