A method of roasted coffee beans treatment capable of reducing acidity component of the roasted coffee beans, improving the extraction ratio thereof and drawing out superior flavor originating from coffee and steam treated roasted coffee beans using the method. In the method of roasted coffee beans treatment, a steam treatment is effected on the roasted coffee beans by supplying steam thereto under a flowing condition thereof. More particularly, the roasted coffee beans are accommodated in a bean accommodating portion having a steam supply passage and a steam exhaust passage and the steam treatment is effected by flowing the steam from the steam supply passage to the steam exhaust passage such that the steam is exhausted from the steam exhaust passage at an outlet pressure higher than theatmospheric pressure. The steam treated roasted coffee beans have received a steam treatment by supplying steam to the beans under a flowing condition thereof, the resulting roasted coffee beans having an extraction ratio of 35% or more, a sum of an amount of formic acid and an amount of acetic acid relative to the roasted coffee beans being 0.25 weight % or less.