To perform modifying treatment of construction surplus soil without producing industrial waste.

Soil improving equipment has a rotary crusher 1. The rotary crusher 1 is a combination of rolls 9 and 9 whose circumferential surfaces have crushing teeth 10; the crushing teeth 10 of the roll 9 are a combination of bars 10a and bits 10b; the bars 10a and the bits 10b are alternately mounted on the circumference of each roll 9; the bar 10a is a short column; and the bit 10b forms a tooth shape. The rotary crusher 1 crushes massive matter, included in the construction surplus soil, into fine particles, before adding a soil improving material to the construction surplus soil, efficiently performs the reforming treatment without imposing a burden on a paddle mixer of mixing equipment, and performs crushing treatment of a rock, a concrete mass, etc., included in soil to be treated, along with the modifying treatment of the soil to be treated.