To provide a soil conditioner which has a stabilized effect of preventing scab and hardly influences the succeeding cropping.

This conditioner contains 13-21wt.% (in terms of aluminum oxide) solid aluminum sulfate with such a particle size distribution that particles having sizes lower than 5mm, sizes of 5mm or higher but lower than 8mm, sizes of 8mm or higher but lower than 10mm, sizes of 10mm or higher but lower than 20mm, and sizes of 20mm or higher account for 30-100wt.%, 0-70wt.%, 0-50wt.%, 0-20wt.%, and 0-20wt.%, respectively, of all the particles.