The hydraulic cylinder mechanism has a main piston which has a piston portion, two sub-pistons which is so located that the sub-pistons can hold the piston portion, control pressure chambers which are formed between the sub-piston and the piston portion, and holding pressure chambers which are formed at behind of the sub-piston. The hydraulic cylinder mechanism controls automotive rear wheel alignment when the main piston moves axially according to the pressure in the control pressure chambers and can maintain its neutral position when the pressure in the holding chamber is applied to the sub-piston so that holds the piston portion.