To propose a method for improving soil generated by construction.

According to the method for improving soil generated by construction, the generated soil is charged into an earth hopper 14 via a size screening means 10 for screening gravel having a predetermined size or more out of the generated soil, and the weight of the charged soil to be treated is measured by a measuring means 42, followed by adding a predetermined quantity of an addition agent stored in an addition agent storage means 20, based on the result of measurement. Thereafter, the soil to be treated with the addition agent added thereto is mixed and agitated by a mixing/agitating means 30, to thereby obtain improved soil. In the method, to obtain the improved soil, a cement hardener is employed as the addition agent, which is then added only in a quantity corresponding to the contents of silt and clay contained in the soil to be treated.