A milk raw material is fermented by using Lactococcus lactis not having cell wall-enveloped proteinase and a Bifidobacterium bacterium. The Lactococcus lactis is, for example, a Lactococcus lactis having a property that, when this bacterium and the Bifidobacterium bacterium are inoculated into a medium containing 1% (W/W) of glucose and 10% (W/W) of reduced skim milk powder in amounts of 5.0×106 to 2.0×108 CFU and 1.0×107 to 3.0×109 CFU per 1 ml of the medium, respectively, and cultured, and the medium is rapidly cooled to 10° C. from culture temperature when pH of the medium becomes 4.6 to 5.5, and stored at 10° C. for 2 weeks, survival rate of the Bafidobacterium bacterium is maintained to be 30% or more.
