PURPOSE: To obtain minute crystal particles by precipitating a substance to be crystallized by a method wherein the substance to be crystallized is dissolved in a solvent, and a raw solution is supplied to a long heating pipe having a solid-gas separator connected to the other end thereof to be evaporated to dryness within a short time, and the formed product is injected in a separation chamber along with steam.

CONSTITUTION: The raw solution from a raw solution tank 1 is supplied to a long heating pipe 3 by a quantitative pump 2 having a solid-gas separator 4 connected to the other end thereof and the steam passing through the filter material 5 of the separator 4 is discharged from a discharge port 6 to be sent into a condenser 7. A solvent recovery tank 8, a pump 9 for sending a recovered solvent and a vacuum pump 10 are connected to the condenser 7 and a mixer 11 is arranged under the solid-gas separator 4 and a vacuum pump 12 is connected to the mixer 11 to hold the mixer 11 and a separation chamber 4a to a vacuum state. Further, by providing a discharge valve 13 and a partition valve 14 to the mixer 11, crystal particles reduced in heat history and oxidative deterioration are obtained.