A shock absorber is provided with a cylinder, a piston inserted into the cylinder and demarcating an interior of the cylinder into an extension side chamber and a compression side chamber, a piston rod joined to the piston, a damping passage, provided in the piston rod, that communicates with the extension side chamber and the compression side chamber, and a damping force adjustment valve provided in the damping passage. The damping force adjustment valve includes a damping force adjustment unit and a solenoid that drives the damping force adjustment unit to adjust a flow channel resistance. The piston rod includes a yoke into which the damping force adjustment valve is inserted, and a piston holding member mounted on the yoke. The yoke includes a through-hole opening from a side of the yoke and leading to the interior, and a groove provided on a perimeter of the yoke, extending from an anti-piston end, and leading to the through-hole.