A force sensor according to embodiments includes a light-emitting unit, a pair of first light detectors, a reflector, and a first frame. The light-emitting unit emits diffuse light. The first light detectors are arranged in a first direction with the light-emitting unit interposed therebetween. The reflector is arranged to face the light-emitting unit on an optical axis of the light-emitting unit and reflects the diffuse light emitted from the light-emitting unit toward the first light detectors. The first frame is deformed in the first direction so that a reflection range of the diffuse light reflected by the reflector is displaced in the first direction.