A force sensor includes a base unit, an elastic supporting unit, an action unit supported by the elastic supporting unit, and a detection unit that detects at least one of an external force acting on the action unit and a moment acting on the action unit. The detection unit includes a light source, a diffraction grating, a photodetector array that receives an interference image formed by light that has been emitted from the light source and diffracted by the diffraction grating and outputs signals having different phases, and a calculation unit that calculates a displacement of the action unit with respect to the base unit on the basis of the signals and calculates at least one of the external force and the moment acting on the action unit on the basis of the displacement.