PURPOSE: To provide a multistage filter decreased in cost, enhanced in filtering efficiency, reduced in the use amt. of a rinse soln. and capable of preventing the deviation of a flow rate (deflected flow) to each of filter chambers.

CONSTITUTION: At the time of filtering (1), a liquid containing a solid is passed through the filter parts 2a, 2b of upper and lower stage filter chambers A, B downwardly through liquid injection pipings 4, 4a to collect the solid in the liquid while a filtrate is discharged out of a container 1 from liquid discharge pipings 5b, 5a and opening and closing valves 16 to 26 are appropriately operated to pass the liquid through one of the upper and lower stage filter chambers A, B or both of them in succession to perform filtering work. At the time of the backwashing of the filter parts 2a, 2b (2), a washing soln. is passed through the filter parts upwardly and the collected solid is removed to the outside of the container along with the washing soln. At the time of the rinsing work of the filter parts 2a, 2b (3), a rinse soln. is sent to the upper and lower stage filter chambers A, B from the liquid injection pipings 4, 4a and passed through the filter parts 2a, 2b downwardly to condition the filter parts 2a, 2b and discharged out of the container 1.