A front fork, which is interposed between a vehicle body and an axle to restrain a change in vehicle attitude, comprises a fork body (101) including a reservoir chamber (106) partially filled with gas and performing an expansion and contraction operation, a reservoir tank (102) partially filled with gas and communicating with the reservoir chamber (106) through a flow path (103) in which hydraulic oil flows, an on-off valve (35) switching between opening and closing of the flow path (103), and a relief valve (40) accepting flow of hydraulic oil from the reservoir chamber (106) toward the reservoir tank (102) when a pressure of the reservoir chamber (106) reaches a predetermined pressure.