An auxiliary device for an agricultural working machine includes a hydraulic pump unit designed to pump a hydraulic fluid at a predetermined working pressure; a drive unit connected to the hydraulic pump unit that drives the hydraulic pump unit at the working pressure; a hydraulic drive having a drive-fluid inlet connected to a pump-fluid outlet of the hydraulic pump unit via a pressure line (P1, P2) and a drive-fluid outlet connected to a pump-fluid inlet via a supply line (S); and a fluid exchange device having a fluid supply line connected to the supply line (S) for a controlled supply of the hydraulic fluid from a hydraulic circuit of the working machine and a fluid discharge line connected to the supply line (S) upstream of the fluid supply line for the controlled discharge of the hydraulic fluid from the supply line (S) into the hydraulic circuit.