Four shock absorbers are connected to a control cylinder. The control cylinder includes a housing body portion having two cylinder chambers which are divided by a partition wall portion; and a piston assembly which is formed by coupling two pistons with each other using a coupling rod. Two outer side control chambers and two inner side control chambers are connected to respective absorber chambers. Pressure receiving areas of outer side pressure-receiving surfaces and inner side pressure-receiving surfaces of the pistons and damping characteristics of the shock absorbers are set such that a direction in which the piston assembly moves in a region where an operation speed is low is opposite to a direction in which the piston assembly moves in a region where the operation speed is high.