To provide an inexpensive detent mechanism of a solenoid switching valve by which a size of an entire valve can be reduced by arranging a detent member on one end part of a spool slidably inserted in a valve body, and which can maintain stable locking holding force even when used for a long period of time.

Washers 13, 14 are inserted in a large diameter of a stepped recessed part 11 formed on an inside of a plug 26 screwed in a valve body 23, and the washers 13, 14 are slidably inserted in an outer diameter part of a spool pin 17 of the spool 25. An approximately U-shaped spring piece 15, for example, is supported between the washers 13, 14. The spring piece 15 is engaged in a groove 18a, or 18b formed on the spool pin 17, and a switching position of the spool 25 by switching of coil parts 45a, 45b is maintained.