A steam pressure reducing and conditioning valve for passing a superheated steam S inflowing from a first port 1 through a pressure reducing section 2, and, supplying subcooled water mist W and discharging desuperheated and depressurized steam S2 from a second port 3, wherein a first nozzle 4 for supplying mist W is provided in proximity to the pressure reducing section 2. The nozzle 4 injects subcooled water mist in a planar pattern r perpendicular to the flow of depressurized steam S1. Said first nozzle 4 is disposed such that there is a predetermined distance L between the jet pattern r of moisture W injected from the nozzle and the pressure reducing section 2.