An anti-obesity agent containing, as an active ingredient, a microorganism which belongs to the species Lactobacillus reuteri and is capable of producing lipases having the amino acid sequences respectively depicted in SEQ ID NO: 1, 3 or 5 or amino acid sequences having deletion, substitution or addition of one or more amino acids in the amino acid sequences respectively depicted in SEQ ID NO: 1, 3 or 5. The anti-obesity agent enables a patient to take a normal meal yet preventing the absorption of a fat into the body which is the primary cause of obesity.