Provided are new reduced-pressure spray-drying method and device suitable for drying and powdering a liquid raw material containing a material that is easily heat-denatured, including, for example, a food raw material and a medicine raw material. The method and device comprise: a device main body maintained under a reduced pressure and having a spray nozzle an overheated water vapor supplying means for supplying overheated water vapor to the spray nozzle a liquid raw material supplying means for supplying a liquid raw material to the spray nozzle a cooling means for cooling the overheated water vapor discharged from the device main body and vapor vaporized from the liquid raw material and collecting the vapor as condensed water a depressurizing means for maintaining the inside of the device main body under reduced pressure via the cooling means and a product collecting means for collecting a powder product produced in the device main body. The overheated water vapor supplied from the overheated water vapor supplying means and the liquid raw material supplied from the liquid raw material supplying means are simultaneously sprayed from the spray nozzle into the device main body, and the liquid raw material is atomized within the device main body. Further, the atomized raw material produced by atomizing the liquid raw material is subjected to perform heat exchange with the overheated water vapor, so that the liquid raw material is dried and powdered.
