In a force sensor, a cylindrical movable body can be moved with respect to a cylindrical main body. A strain body is fixed to the main body and the movable body, and can be deformed in accordance with the movement of the movable body. Strain sensors are provided on the strain body. At least three circular openings are provided in the circumferential surface of the movable body at equal intervals. Stoppers are respectively arranged inside the openings, and each of which includes a first side surface having a first outer diameter smaller than an inner diameter of the opening, and a second side surface having a second outer diameter smaller than the first outer diameter. Fixing members fix the stoppers to the main body.