To enable generation of stable damping force, and to guarantee sealing performance while guaranteeing prescribed aligning or sliding performance on a rod body passing through an axial core part.

Seal structure of a cylinder head part comprises a bearing member 4 provided on the axial core part of a head member 3 for sealing an opening end of a cylinder body 1, through which the rod body 2 passes, with an inner periphery in slide contact with an outer periphery of the rod body 2 with sliding clearance, and a seal ring member 5 provided on the axial core part of the head member, with the inner periphery in slide contact with the outer periphery of the rod body 2, and in series from an outside of the cylinder body 1 to the bearing member 4 along an axial direction of the rod body 2.