An object of the present invention is to provide a method for producing a fermented milk, in which fermentation is accelerated without using a fermentation accelerator or the like and a novel fermented milk obtained by the production method having a hard texture that does not collapse during the distribution stage while having thickness and mildness which are not exhibited by conventional products. As a result of study, it was found that the fermentation efficiency can be improved by reducing the oxygen dissolved in a raw material mix of the fermented milk at the start of fermentation through replacement thereof with an inert gas, and that fermentation in that condition at usual temperature leads to a method for producing a fermented milk by which the fermentation time is shortened thereby to improve the productivity, and fermentation at a temperature lower than usual leads to a method for producing a fermented milk by which a novel fermented milk that has a thick and mild taste superior to that of a fermented milk with a mild taste produced through conventional low-temperature and long-term fermentation and also has a hard texture that does not collapse during the distribution stage is obtained in usual fermentation time, and leads to such a fermented milk produced by the method. Thus the invention has been completed.