To provide a filtration method capable of suitably preventing a filter from blinding.

In a filtration tank 2 with a filtration space 11 formed therein, a filter 16 composed of a filter cloth with a bag shape is housed by setting its upper-end opening at the upper part of the filtration space 11, and the lower part of the filter 16 is allowed to hang down in the filtration space 11. In the filtration method, the following step is performed successively: a filtration step wherein a liquid to be treated is filtered and the resultant filtrate is discharged; a dehydration step wherein air is fed under pressure to the supply side 11a of the liquid and the liquid staying in the filtration space 11 is removed; and a backwash step wherein air is fed under pressure to the discharge side 11b of the liquid and is caused to permeate the filter 16. In the backwash step, a filtered substance 40b can be separated by the action of both the pressure of air blowing out of the inside surface of the filter 16 and the deformation or vibration of the filter cloth surface, enabling blinding to be efficiently prevented.