A filtration device (3) has: a housing case (15) having a water inlet unit and a water outlet unit arranged on one end side thereof； and a membrane module (17) provided inside this housing case (15). A first flow path (31) for causing raw water that has flowed in from the water inlet unit (21) to flow further to the other end side of the housing case (15) than the membrane module (17), and a second flow path (33) for causing the raw water that has flowed further to the other end side of the housing case (15) along this first flow path (31) to pass through the membrane module (17) and flow to the water outlet unit (23) are provided inside the housing case (15). A spacer (19) is provided on the upstream side of the membrane module (17) in the second flow path (33).
