To provide a solenoid valve capable of realizing high durability, by securing high sealability and the smooth movement over a long period, by devising a structure of a piston sliding in a housing.

This solenoid valve has a fluid control part 1 for slidingly arranging the piston 6 in the housing 7 for opening and closing a valve seat 9 of a communicating port 5 for communicating a primary passage 3 and a secondary passage 4, forming an introducing passage in the piston 6 for introducing fluid from the primary passage 3 into a pressure chamber 11 and forming a discharge passage 17 for discharging the fluid to the secondary passage 4 from the pressure chamber 11, and an electromagnetic opening-closing part 2 for opening and closing the discharge passage 17 by the electromagnetic action. A metal seal is applied between the piston 6 and the housing 7. Packing 14 is arranged on a peripheral surface of the piston 6 for checking intrusion of the fluid via a space with the housing 7. An annular ring-shaped groove 30 and a groove 31 are respectively formed by sandwiching the packing 14, and a stepped part 16 is also formed in a housing side end part of the piston 6.