SmFe is a kind of giant magnetostrictive material. Though Terfenol-D has a positive magnetostriction constant, SmFe has a negative magnetostriction constant. Furthermore, the permeability of SmFe is bigger than the permeability of a Tb system material. Since the permeability is big, it is expected that the merit is big, when a sensor device is constructed using SmFe. This paper describes an SmFe thin film and a method for introducing stress into the SmFe thin film. Next, the results of measuring the magnetic characteristic using VSM, while the stress is applied, are shown. Finally, it is shown that a highly sensitive force sensor can be constructed using an SmFe thin film, because the differential permeability greatly changes on the SmFe thin film, when tensile stress was applied, from the measured magnetic characteristic.