To effectively suppress vertical resonance of a car body by means of a shock absorber in a suspension of a vehicle.

A shock absorber 1 of a suspension for a vehicle comprises a cylinder 4, a piston 5, a hollow piston rod 6, a resonance part 7, and so on. The piston 5 is provided with a damping force generating part 10. A movable mass body 12 is supported by upper and lower springs 13 in a case 11 of the resonance part 7 so as to move in the almost vertical direction. A control part 14 is elongated from a lower surface of the movable mass body 12 to a damping force generating part 10 through a hollow part of the piston rod 6. A plurality of axially elongating oil passages are formed on the inner surface of the case 11 facing the movable mass body 12. When the movable mass body 12 vibrates in the almost vertical direction under a resonant state accompanied by the vertical resonance of the car body, vibration damping force of the damping force generating part 10 is intensified by the control part 14.