In a shock absorber of a vehicle, when a moving speed of a piston rod in relation to a cylinder tube is slow and first and second input forces are externally applied to the shock absorber, damping forces of pressure side and extension side first damping force generating devices are larger than that of pressure side and extension side second damping force generating devices. On the other hand, when the moving speed is fast, the damping forces of the pressure side and the extension side second damping force generating devices are larger than that of the pressure side and the extension side first damping force generating devices. A gas enclosure chamber filled with gas is connected to a first chamber through a free piston.