PURPOSE: To limit change in quality and deterioration of soybean milk to the minimum, and to enable removal of heat-resistant, harmful bacteria completely, by selecting properly temperature and time of sterilization of soybean milk in a state where a saccharide is added to it.

CONSTITUTION: Soybean milk of lactic acid fermentation is prepared by a component preparation process wherein a saccharide is added to soybean milk extracted from soybeans by a conventional procedure, by a sterilization process wherein soybean milk is heated in the sterilization pot 1 and 110W120°C for 20W30min by a deodorizing process wherein the pot 1 is rapidly decompressed, by a cooling process, and by a fermentation process with lactic acid bacteria. Namely, since temperature and time of sterilization are properly selected, even if soybean milk is sterilized under heating after the saccharide required to improve lactic acid fermentation and taste is added to it, deterioration in quality caused by browning of the saccharide will not occur, and heat- resistant bacteria derived from soil can be removed completely. The exhaust vent 11 of the heated pot 1 is opened, the abrupt pressure drop is produced in the inside of the pot, and a volatile component causing smell is discharged, so effective deodorization can be carried out during the cooling process without providing specifically a deodorization process.