SHOCK ABSORBER

A shock absorber includes a suction passage (3) configured to permit only a flow from a reservoir (R) toward a compression-side chamber (R2), a rectification passage (4) configured to permit only a flow from the compression-side chamber (R2) toward a extension-side chamber (R1), and a variable valve (V) configured to permit only a flow from the extension-side chamber (R1) toward the reservoir (R). A large chamber (16) serving as a compression-side pressure chamber that communicates with the compression-side chamber (R2) and an outer periphery chamber (17) serving as a extension-side pressure chamber that communicates with the extension-side chamber (R1) are partitioned in the shock absorber by a free piston (5) that moves slidably within a bottom member (11) serving as a housing. A compression-side pressure-receiving area (A1) of the free piston (5) is larger than an extension-side pressure-receiving area (B1). Therefore, even in the uniflow shock absorber in which the extension-side chamber (R1) and the compression-side chamber (R2) are at equal pressures during the contraction operation, the damping force is reduced under conditions in which high frequency is input since the free piston (5) moves downward.