To provide a filtering method and a filtering device supplying a filtering layer hardly causing clogging (a filtering layer capable of releasing clogging even if clogging occurs) in solid/liquid separation of a material with a particle size of several microns to submicrons, and easily switching or exchanging the filter medium layer.

This filtering method of a batch switching type switches the filtering medium layer packed with roughly spherical particles having particle sizes larger than a certain value to another clean filtering medium layer for filtering. The continuous filtering method takes out particles under using for filtering from the filtering medium layer packed with roughly spherical particles having particle sizes larger than a certain value, and replenishes clean particles for filtering.