Abstract: A damper includes a cylinder into which magneto-rheological fluid is sealed, a first fluid chamber and a second fluid chamber, a throttle passage, an electromagnetic coil, and a spacer. The first fluid chamber and the second fluid chamber are partitioned by a piston core in the cylinder. The throttle passage is formed between an inner peripheral surface of the cylinder and an outer peripheral surface of the piston core. The throttle passage communicates between the first fluid chamber and the second fluid chamber. The throttle passage provides a resistance to a flow of the passing magneto-rheological fluid. The electromagnetic coil generates a magnetic field acting on the magneto-rheological fluid flowing through the throttle passage. The spacer is mounted to the piston core and is configured to adjust a length of the throttle passage.