A shock absorber includes: a cylinder which is filled with a fluid; a piston valve which includes a valve seat dividing an inner space of the cylinder, a passage which is formed in the valve seat and through which the fluid passes, and a valve disposed to cover the passage and interfering with a flow of the fluid; a performance controller which is disposed in the cylinder to control at least one of a spring constant, a damping force, or a combination thereof; and a piston support which is connected to the piston valve and exposed to an outside.