Shock absorber

In a shock absorber (1) in which a bypass flow path (21) communicating oil chambers (14A, 14B) in both sides of a partition wall body (31) is provided within a casing (10), a fixed partition wall member (23) is provided between two movable partition wall members (22A, 22B) within the bypass flow path (21), viscous fluid chambers (24A, 24B) receiving a viscous fluid changing a shear stress in response to a magnetic field or an electric field are sectioned respectively between two movable partition wall members (22A, 22B) and the fixed partition wall member (23), and a flow path (25) communicating the viscous fluid chambers (24A, 24B) in both sides is provided in the fixed partition wall member (23), and a means (an electromagnetic coil (26)) for changing the shear stress of the viscous fluid by applying a magnetic field or an electric field to the viscous fluid is provided.