Disclosed herein is a solenoid valve having a valve seat assembly manufactured as a single body such that the valve seat assembly is simply fitted in a valve housing. The valve seat assembly comprises a valve seat, a filter, and a sealing plate. The valve seat assembly is disposed at one end of a housing. The valve seat comprises a first orifice formed such that the first orifice is opened and closed as a plunger is moved forward and backward, and a second orifice formed such that the second orifice is arranged in parallel with the first orifice. The sealing plate is provided at the center thereof with a through-hole, which communicates with the first orifice of the valve seat. The sealing plate is disposed in the valve seat such that the sealing plate is not separated from the valve seat by means of the filter. The sealing plate is moved toward the first orifice by the pressure of a fluid close the second orifice. In this way, the sealing plate serves as a check valve.