The present invention relates to: fermented milk that does not undergo the increase in an acid level; a method for producing the fermented milk; Lactobacillus delbrueckii subsp. bulgaricus OLL1171 (NITE BP-01569) which is a lactic acid production strain useful for the production of fermented milk that does not undergo the increase in an acid level; and a method for screening for a lactic acid production strain useful for the production of fermented milk that does not undergo the increase in an acid level.