Force sensor

A force sensor of the present invention includes: a supporting body arranged on an X-Y plane; a deformation body arranged opposite to the supporting body and having a deformation part elastically deformed by an action of a force to be detected; a fixed electrode arranged on the supporting body; a displacement electrode provided to the deformation part of the deformation body in such a manner as to face the fixed electrode with which it forms a capacitive element; and a detection circuit that outputs an electrical signal representing the acting force based on a variation amount of a capacitance value of the capacitive element, wherein the capacitive element includes a first capacitive element and a second capacitive element, and the detection circuit determines whether the force sensor is normally functioning based on a first electrical signal corresponding to a capacitance value of the first capacitive element, a second electrical signal corresponding to a capacitance value of the second capacitive element, and an added electrical signal corresponding to a sum of the capacitance values of the first and second capacitive elements.