A strain detector includes a bridge circuit having at least two strain resistance elements, a substrate, a first fixed member, and a second fixed member. The substrate has a circuit portion electrically connected to the strain resistance elements. The strain resistance elements are arranged on the substrate. The first fixed member is fixed to a center of an area, where an outer periphery of the area is set at a position at which the strain resistance elements are arranged. The second fixed member is fixed outside the position, where the strain resistance elements are arranged at the substrate. A center of an axis of the first fixed member, a center of an axis of the second fixed member, and the center of the area are positioned on a straight line, and the first fixed member and the second fixed member are arranged on two mutually opposed surfaces of the substrate.