To provide a method for treating a pollutant, in which the pollutant is decomposed and treated without necessitating a large amount of bacterial beds and also without scattering contaminated soil in the surroundings.

A bacterial bed such as the bacterial bed of eatable bacteria having decomposing capacity of the pollutant or a waste bacterial bed is crushed and made to a pulverized state. The powdery bacterial bed is injected into polluted soil and added by using a device 5 equipped with a tank 1 housing the powdery bacterial bed, a force-feeding means 2 consisting of a force-feeding pipe 2A and a pump 2B for force-feeding the powdery bacterial bed from the tank 1, a platelike head 3 connected to the tank 1 via the force-feeding means 2 and a plurality of hollow tubular projecting parts 4. When the head 3 is pushed on the soil surface and the head surface is allowed to abut on the soil surface, the tubular projecting parts 4 are inserted into soil by only the projecting length. When the pump 2B is driven in this state, the powdery bacterial bed housed in the tank 1 is injected into soil from the tubular projecting parts 4 through the force-feeding pipe 2A.