A shock absorber comprising: a cylinder in which a hydraulic fluid is sealed; a free piston slidably inserted into the cylinder, the free piston partitioning inside of the cylinder into a liquid chamber (110, 120) and a gas chamber; a piston slidably inserted into the cylinder, the piston partitioning the liquid chamber (110, 120) into an extension-side chamber and a contraction-side chamber; a piston rod inserted movably into and out of the cylinder, the piston rod being coupled to the piston; a rod guide fitted onto an end portion of the cylinder on the liquid chamber (110, 120) side, the rod guide slidably supporting the piston rod via a bush disposed on an inner periphery; and an oil seal (8, 12, 13) disposed on an opposite side of the liquid chamber (110, 120) on the rod guide, the oil seal sealing (8, 12, 13) between the piston rod and the cylinder, wherein the rod guide includes: a housing portion disposed on a surface of the oil seal (8, 12, 13) side, the oil seal (8, 12, 13) including a seal lip (8b, 12b, 13b) housed in the housing portion; and a depressed portion depressed on a bottom surface of the housing portion, the depressed portion being formed toward an outer periphery from a starting point located apart from the piston rod by 1/2 or more of a distance in an axial direction between the bottom surface and a flat portion (8e, 12e, 13i) of the oil seal (8, 12, 13) in a radial direction closest to the piston rod, wherein the bush is disposed to be flush with the bottom surface of the housing portion, or to project from the bottom surface, characterized in that the depressed portion is configured to accumulate contamination and that the starting point of the depressed portion of the housing portion is disposed in a range to a position apart from the piston rod by a distance in an axial direction between the bottom surface of the housing portion and the flat portion (8e, 12e, 13i) of the oil seal (8, 12, 13). a cylinder in which a hydraulic fluid is sealed; a free piston slidably inserted into the cylinder, the free piston partitioning inside of the cylinder into a liquid chamber (110, 120) and a gas chamber; a piston slidably inserted into the cylinder, the piston partitioning the liquid chamber (110, 120) into an extension-side chamber and a contraction-side chamber; a piston rod inserted movably into and out of the cylinder, the piston rod being coupled to the piston; a rod guide fitted onto an end portion of the cylinder on the liquid chamber (110, 120) side, the rod guide slidably supporting the piston rod via a bush disposed on an inner periphery; and an oil seal (8, 12, 13) disposed on an opposite side of the liquid chamber (110, 120) on the rod guide, the oil seal sealing (8, 12, 13) between the piston rod and the cylinder, wherein the rod guide includes: a housing portion disposed on a surface of the oil seal (8, 12, 13) side, the oil seal (8, 12, 13) including a seal lip (8b, 12b, 13b) housed in the housing portion; and a depressed portion depressed on a bottom surface of the housing portion, the depressed portion being formed toward an outer periphery from a starting point located apart from the piston rod by 1/2 or more of a distance in an axial direction between the bottom surface and a flat portion (8e, 12e, 13i) of the oil seal (8, 12, 13) in a radial direction closest to the piston rod, wherein a housing portion disposed on a surface of the oil seal (8, 12, 13) side, the oil seal (8, 12, 13) including a seal lip (8b, 12b, 13b) housed in the housing portion; and a depressed portion depressed on a bottom surface of the housing portion, the depressed portion being formed toward an outer periphery from a starting point located apart from the piston rod by 1/2 or more of a distance in an axial direction between the bottom surface and a flat portion (8e, 12e, 13i) of the oil seal (8, 12, 13) in a radial direction closest to the piston rod, wherein the bush is disposed to be flush with the bottom surface of the housing portion, or to project from the bottom surface, characterized in that the depressed portion is configured to accumulate contamination and that the starting point of the depressed portion of the housing portion is disposed in a range to a position apart from the piston rod by a distance in an axial direction between the bottom surface of the housing portion and the flat portion (8e, 12e, 13i) of the oil seal (8, 12, 13).