Filtration apparatus

A filtration apparatus for performing solid-liquid separation by immersing a plurality of hollow fiber membranes in a to-be-treated liquid containing a suspended component so that the treated liquid permeates the hollow fiber membranes. The filtration apparatus includes the hollow fiber membranes folded double; a treated liquid collection means communicated with an open-side end of each of the hollow fiber membranes; a holding member for holding a bent portion at an other-end side of each of the hollow fiber membranes with a gap formed between the bent portion of each of the hollow fiber membranes and the holding member; and a gas-jetting means for jetting a cleaning gas from the other-end side of each of the hollow fiber membranes to the open-side end of each of the hollow fiber membranes. A gap for flowing the gas jetted by the gas-jetting means is formed between the hollow fiber membranes held by the holding member and the holding member or/and on at least one part of gaps between the hollow fiber membranes.