TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The coating is diamond-like carbon coating, chromium nitride coating, titanium nitride coating, gold coating, MOS2-coating, nickel-phosphorus plating, or nickel-boron plating.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Property: The surface roughness of the valve seat and the valve member is less than or equal to1 micronsRa. Preferred Component: The valve member is located to freely slide in an accommodating member (106). A coating is formed on the surface of the valve member to reduce friction between the valve member and the accommodating member. It is formed through a treatment of physical vapor deposition coating, baking, or plating. The valve includes a solenoid, a main valve seal and a pilot valve (122) seat, a main valve body (130) switchable between a closed state where the main valve body contacts the main valve seat and an open state where the main valve body is separated from the main valve seat, and a pilot valve body switchable between a closed state where the pilot valve body contacts the pilot valve seat and an open state where the pilot valve body is separated from the pilot valve seat. The pilot valve body is switched between open and closed states in accordance with excitation and de-excitation of the solenoid. A plunger (112) operates in accordance with excitation and de-excitation of the solenoid. It is coupled to the main valve body and valve seat. The pilot valve seat has a projection (120) with a distal end surface. The valve body and a diaphragm define a pressure reducing chamber having a valve hole (192) provided with the valve seat.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The coating is diamond-like carbon coating, chromium nitride coating, titanium nitride coating, gold coating, MOS2-coating, nickel-phosphorus plating, or nickel-boron plating.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The synthetic resin is polyamide resin, polyether ether ketone resin, or polyfluoroethylene resin. The polyimide resin is VESPEL. The coating is polytetrafluoroethylene coating.