To surely and stably adjust the vehicle height except when a period of vehicle body behavior is short.

This shock absorber is provided with a heater 16 heated by supplying an electric current by operation of a vehicle height detecting switch 18 at vehicle height lowering time, a filter circuit 27 for restricting electric current supply to the heater 16 when a period of an ON-OFF signal of the vehicle height detecting switch 18 is short and a pressure chamber 17 formed between a cylinder 1, a piston rod 2 and a case 6 and housing a pressure medium. The vehicle height is adjusted by relative displacement of the cylinder 1 and the piston rod 2 by increasing pressure in the pressure chamber 17 by heating and expanding the pressure medium by the heater 16 only when the vehicle height body behavior becomes stable.