A filter apparatus is equipped with a first body, a case unit connected to a lower part of the first body, and a filter unit, which is accommodated in the interior of the case unit. The case unit is made up from an outer case, which is formed as a bottomed cylinder from a light-permeable transparent material, and an inner case that is inserted into the interior of the outer case. The case unit is inserted into an installation hole that opens on the lower part of the first body, and by rotation thereof, projections and retaining walls provided on an outer circumferential surface of the case unit are made to engage with support members provided in the installation hole, to thereby result in a connected state.