To provide a solenoid valve capable of using a small solenoid regardless of size of a piston for driving a main valve.

The outer periphery of the piston 10 for driving a main valve element 5 is completely sealed by a V packing 11 to eliminate pressure introduction to a piston chamber 18 from the periphery of the piston 10. A high pressure introduction control valve including a passage 14, a valve seat 13, a valve element 16, and a passage 19 is disposed between a fluid inlet 2 and the piston chamber 18. The high pressure introduction control valve is inversely operated in cooperation with a pilot valve for releasing pressure of the piston chamber 18 to a low-pressure fluid outlet 3. Pressure is not introduced from the periphery of the piston 10 to the piston chamber 18, so that a pilot valve hole can be kept small regardless of diameter of the piston 10. The solenoid for driving a pilot valve may be kept small even when the diameter of the piston 10 is increased, so that the compact and inexpensive solenoid valve can be provided.