PURPOSE: To provide a shock absorber in which a damping force variable range on the compression side is increased and which has such characteristics as 'a soft mode on the compression side/a hard mode on the expansion side' and 'a hard mode on the compression side/a soft mode on the expansion side'.

CONSTITUTION: A port 11 on the compression side provided with a check valve 13 opened toward the upper working oil chamber A side is formed in a piston 2. Two passage are formed wherein one is a passage running from the port 11 on the compression side to a lower working oil chamber B through a piston rod 4 while the other, a passage which is communicated in a crossing manner with the passage after it runs from the upper working oil chamber through the piston rod and communicated with the lower working oil chamber through a valve 28 on the compression side having a function to check the expansion side. A switch valve 16 having at least three on-off modes is arranged in the piston rod. Further, a check valve 8 is disposed to a base valve 9, while an oil passage 38 through which the upper working oil chamber is communicated with a reservoir chamber C is provided, and a valve 41 used in common on the expansion side and the compression side is located in the oil passage.