To reduce a space required for assembling-in by reducing diameter of a piston of an air spring attached to a shock absorber to constitute a strut assembly.

This shock absorber has an outer cylinder and a shock piston 22 and a piston rod 24 in the outer cylinder. The outer cylinder has a shock mount 30 attached to a wheel of a vehicle. An air spring assembly 12 has an upper mount attached to a vehicle body member and a lower mount attached to the outer cylinder. An air spring piston 40 is attached to the upper mount through a bearing assembly to allow relative rotation between the air spring piston 40 and the vehicle body member. A flexible member 42 is extended from the lower mount to a lower end part of the air spring piston 40. The piston rod 24 is attached to the shock piston 22 at one end and to the air spring piston at the other end. An isolator 54 is attached between the piston rod 24 and the air spring piston 40 to suppress shock load to the minimum extent.