Abstract: A control stick is supported in an outer case such that it can be swung in two orthogonal directions. A moving member is fitted to the lower portion of the control stick through a coil spring. The lower end of the moving member is urged by the coil spring to a rotation-symmetrical cup-shaped inside surface of a guide case so as to make pressure contact with the inside surface. The curvature of the inside surface is determined so as to provide such a relationship that a contraction length of the coil spring is proportional to a square root of a tilt angle of the control stick from its neutral position.