A stabilizer apparatus including: (a) torsion bars; (b) a cylinder device including a movable piston and cooperating with the piston to define a fluid chamber accommodating therein a working fluid; and (c) a mechanism configured to hold the piston in a movement end position when the torsion bars are positioned in a neutral angular position, move the piston away from the movement end position when the torsion bars are rotated away from the neutral angular position, and move the piston toward the movement end position when the torsion bars are rotated toward the neutral angular position. The apparatus is capable of switching between a state that allows the piston to be moved in both the opposite directions by allowing outflow and inflow of the working fluid from and into the fluid chamber and another state that allows the piston to be moved only toward the movement end position by allowing only one of the outflow and inflow of the working fluid.