Abstract: A contracted portion having an axial length is formed in the spool hole and a large diameter portion having an axial length is formed in the spool within the spool such that an annular gap is formed there-between. A valve body closes an opening portion of the spool hole. When the valve body is lifted, one of an air pressure source and a drain is connected to an air spring passage via the annular gap. When the spool retreats from the valve body, the other of the air pressure source and the drain is connected to the air spring passage via the annular gap. By setting the lengths at different values, different flow rate characteristics are realized when supplying compressed air to an air spring and discharging air from the air spring.