A shock absorber in the present invention includes: a cylinder; a rod guide fitted to the inner circumference of an end portion of the cylinder; a piston rod movably inserted into the cylinder; a piston connected to the piston rod; and a seal member stacked on the rod guide and through which the piston rod is inserted, wherein the seal member includes: an annular seal case having an annular concave portion on the inner circumference; a seal ring including a base portion and a lip and accommodated in the annular concave portion; an annular seal holder stacked on the rod guide side of the base portion, accommodated in the annular concave portion, and supporting the outer circumference of the seal ring to suppress the diameter enlargement of the lip; and a stopper mounted on the seal case and preventing the seal holder and the seal ring from falling off.