A filter device includes at least one filter unit (10), connectable to a hydraulic circuit (14), with at least one supply line (16), one discharge line (18), and at least one cooling unit (22). The cooling unit is connected to a secondary branch line (20), is connected to the hydraulic unit (14) parallel to the supply line (16), and is supplied with a hydraulic medium by a switching device (24) once a predetermined temperature threshold value of the hydraulic medium to be cooled is attained. A permanent supply (36) for the cooling unit (22) is provided in the direction of flow of the hydraulic medium in the supply line (18) before the switching device (24). This permanent supply (36), connected in parallel to the switching device (24), flows into the secondary branch line (20) to control the volume flow in reverse flow according to the fluid temperature. A partial flow of the hydraulic medium in the supply line directly reaches the cooling unit at low or reduced temperatures, at which the switching device has not yet been actuated to ensure that the cooling unit is permanently supplied with the hydraulic medium.