Present invention enables to mass-produce rich-taste tamari soy sauce with reasonable costs. First step: Moisturizing soybeans. Second step: Steaming the moisturized soybeans. Third step: Shaping the steamed soybeans into nuggets. Fourth step: Mixing a soy flour and seed koji. Fifth step: Putting the mixture on the nuggets. Sixth step: Incubating the nuggets. Seventh step: Putting the incubated nuggets in salt water. Eighth step: Fermenting the nuggets in the salt water. Ninth step: Pressing moromi (solid component of the fermented product). Tenth step: Settling the liquid obtained by pressing the moromoi. Eleventh step: Optionally filtrating raw tamari soy sauce with a reverse osmosis membrane. Twelfth step: Adjusting concentrations of some constituents of the raw tamari soy sauce. Thirteenth step: Pasteurizing the raw tamari soy sauce. Fourteenth step: Settling the pasteurized tamari soy sauce. Fifteenth step: Filtering the supernatant. Sixteenth step: Bottling the tamari soy sauce.
