A damping force adjustable shock absorber that smoothly transfers a magnetic flux while a solenoid is downsized. An electromagnetic damping force adjustment device of the damping force adjustable shock absorber includes a damping force adjustment valve for generating a damping force, and a solenoid for variably adjusting the generated damping force. The solenoid includes a coil configured to generate a magnetic force through supply of current, a cap member having a bottomed tubular shape disposed on an inner peripheral side of the coil, a movable iron core disposed on an inner peripheral side of the cap member, an anchor member configured to attract the movable iron core, a shaft part provided on an inner peripheral side of the movable iron core, and a back-pressure-chamber formation member having a bottomed tubular shape, which is positioned on another end side of the shaft part, and configured to form a back pressure chamber.