To provide a combined precision filtration method in which a filter using a floating filter medium is combined with a leaf filter and merits of both filters are utilized and to provide a filtration apparatus.

A filtration tank (1) is divided by a filter medium spillage preventing plate (2) into a filtration chamber (3) where floating media (10...) are housed and a precoat filter chamber (4) where the leaf filter (17) is housed. Small holes formed on the plate (2) can be opened or closed freely. An original liquid supplying port (11) and a filter medium agitating blade (12) are arranged at the bottom of the chamber (3). A coating material supplying port (26) is opened on the chamber (4). Even if a high-turbidity original liquid is supplied to the tank (1), the suspended matter in the original liquid is captured by a filter medium layer (13) of the chamber (3) and only minute suspended matter contained in the liquid separated in the chamber (3) is filtered by the filter (17) in the chamber (4) so that a leaf filter medium (19) of the filter (17) is hardly clogged, a large quantity of the original liquid can be filtered and precision filtration can be carried out. When the small pores of the plate (2) are closed, the layer (13) can be cleaned independently.