To provide an extendable hydraulic damper having a vehicle height adjusting device capable of enhancing the sealing performance and work efficiency of the vehicle height adjusting device by reducing the working pressure of a hydraulic jack chamber constituting the vehicle height adjusting device.

In the hydraulic damper 10 in which a suspension spring 20 is interposed between a fixed spring support 21 and a movable spring support 23 and the suspension spring 20 is contracted when the hydraulic damper 10 is elongated, a vehicle height adjusting device 30 has a slide guide 32 which expands outwardly in the radial direction on a base of the projecting end of a piston rod 12, a slide member 31 has a large inside diameter slide part 31A sliding along the slide guide 32 and a small inside diameter slide part 31B sliding along the projecting end of the piston rod 12, and the large inside diameter slide part 31 of the slide member 31 forms a hydraulic jack chamber 33 between the projecting end of the piston rod 12 and itself.