DESCRIZIONE
Provided is a filter device for a water tank which can easily perform maintenance, inspection and repair of a pump. This filter device for the water tank to be installed on the outside of the water tank (1) comprises a casing (20) opened to the atmosphere, a filtration zone (Z2) formed in the casing and filtrating the water (W) which flows into the zone (Z2) from the water tank (1), a discharge pump (35) feeding the water (W) passed through the filtration zone (Z2) to the outside of the casing and discharging it into the water tank, a functional part zone (Z1) formed in the casing and separated from the filtration zone (Z2), and a functional part unit (3) having the discharge pump (35) and a unit frame (31) for supporting the discharge pump (35). The functional part unit (3) is removably inserted in the functional part zone (Z1) of the casing (20).