A diaphragm unit detachably attached to a damper body, includes: a cylinder in which a liquid is sealed; a piston rod having a piston sliding inside the cylinder on one end side of the piston rod, in which other end side of the piston rod is extended to an outside of the cylinder; and a rod guide having a bottomed cylindrical shape wherein an insertion opening into which the piston rod is inserted is provided at a bottom portion of the rod guide, the rod guide being fixed to a side of an opening of the cylinder into which the piston is inserted to thereby make the piston rod be slidably inserted in a liquid tight manner, the diaphragm unit further comprising: an end member; an air seal; a rod side member; an annular bump rubber; and a tubular diaphragm, as defined herein.