PROBLEM TO BE SOLVED: To provide a new use of Lactobacillus brevis SBC8803 strain.SOLUTION: A promoter of serotonin secretion contains bacterial cells or their treated product of a strain selected from a group including lactic acid bacteria belonging to Lactobacillus other than lactic acid bacteria belonging to Lactobacillus delbrueckii group and lactic acid bacteria belonging to Pediococcus.