A strain of a lactic bacterium capable of producing a large amount of lactotripeptide; and a fermented milk product which contains a number of components having hypotensive and stress relaxation activities and can be easily eaten and swallowed. More specifically a lactic bacterium belonging to the genus Lactobacillus helveticus, i.e. Lactobacillus helveticus strain CM4 (deposited under the accession number of FERM PB-6060 with National Institute of Bioscience and Human-Technology), which is characterized by having particular mycological properties, producing tripeptides Val-Pro-Pro and/or Ile-Pro-Pro in an amount of not less than 60 νg/ml in terms of Val-Pro-Pro when cultured in animal milk as the medium, containing not less than 9 % by weight (in terms of solid content) of non-fat milk, and exhibiting an extracellular protease activity of not less than 400 U/OD590; and a fermented milk product prepared by fermenting animal milk with the above lactic bacterium.