A shock absorber comprising: a cylinder which has an outer tube and an inner tube provided on an inner side of the outer tube in a radial direction at an interval from the outer tube, and in which oil is sealed; a piston rod of which one end is inserted into the cylinder and the other end is extended outside the cylinder; a piston which is connected to the one end of the piston rod and is provided in the inner tube so as to be slidable along a central axis direction of the inner tube, and which partitions an inner space of the inner tube into a rod-side oil chamber closer to the piston rod and a piston-side oil chamber on an opposite side to the piston rod; a damping force generating unit which controls flow of the oil occurring when the piston slides in the inner tube according to a displacement of the piston rod, to generate damping force; a reservoir that compensates the oil according to a change in advancement volume of the piston rod into the cylinder; a reservoir communication path through which the damping force generating unit and the reservoir communicate with each other; a compression-side communication path through which the piston-side oil chamber and the damping force generating unit communicate with each other; and a compression-side port which is provided in the damping force generating unit, into which the oil flows from the compression-side communication path, and which has a compression-side valve that generates the damping force, wherein a smallest cross-sectional area of the reservoir communication path is smaller than a smallest cross-sectional area of the compression-side port characterized by an extension-side communication path through which the damping force generating unit and an annular passage formed between the outer tube and the inner tube communicate with each other, wherein a smallest cross-sectional area of the extension-side communication path is larger than the smallest cross-sectional area of the reservoir communication path. a cylinder which has an outer tube and an inner tube provided on an inner side of the outer tube in a radial direction at an interval from the outer tube, and in which oil is sealed; a piston rod of which one end is inserted into the cylinder and the other end is extended outside the cylinder; a piston which is connected to the one end of the piston rod and is provided in the inner tube so as to be slidable along a central axis direction of the inner tube, and which partitions an inner space of the inner tube into a rod-side oil chamber closer to the piston rod and a piston-side oil chamber on an opposite side to the piston rod; a damping force generating unit which controls flow of the oil occurring when the piston slides in the inner tube according to a displacement of the piston rod, to generate damping force; a reservoir that compensates the oil according to a change in advancement volume of the piston rod into the cylinder; a reservoir communication path through which the damping force generating unit and the reservoir communicate with each other; a compression-side communication path through which the piston-side oil chamber and the damping force generating unit communicate with each other; and a compression-side port which is provided in the damping force generating unit, into which the oil flows from the compression-side communication path, and which has a compression-side valve that generates the damping force, wherein a smallest cross-sectional area of the reservoir communication path is smaller than a smallest cross-sectional area of the compression-side port characterized by an extension-side communication path through which the damping force generating unit and an annular passage formed between the outer tube and the inner tube communicate with each other, wherein a smallest cross-sectional area of the extension-side communication path is larger than the smallest cross-sectional area of the reservoir communication path.