PURPOSE: To provide the subject new culture base containing milk as a nitrogen source and a carbon source, calcium carbonate as an agent for suppressing the depression of pH and a soluble Mg salt as an agent for promoting the proliferation of lactobacillus and capable of giving a lactobacillus starter having high and stabilized activity at a low cost.

CONSTITUTION: This culture base for the preparation of a lactobacillus starter contains a milk (preferably skim milk or whey powder) as a nitrogen source and a carbon source. The culture base is incorporated with calcium carbonate or calcium phosphate in an amount of preferably ≥1.5% for suppressing the lowering of pH caused by the lactic acid fermentation and with ≥150mM of a soluble magnesium salt (preferably magnesium sulfate or magnesium chloride) to promote the proliferation of lactobacillus. The amount of the skim milk or the whey powder is preferably 3.5-5%.