From a device (46) for opening pressed bales of fiber material set up in a row (39, 40), the opened fiber material is conveyed pneumatically (55) to a hopper feeder (1). A receiving chamber (13) and upwardly extending inclined spiked feed lattice (3) are provided in hopper feeder (1) for delivering fiber to a processing machine via outlet (8). The delivery of the fiber material, removed continuously from the row of bales, to receiving chamber (13) of hopper feeder (1) is performed transversely to the latter, and in parallel to spiked feed lattice (3). In another embodiment a filling chamber (13a) may be advantageously compartmentalized by transverse walls (57, 58) and provided with a bottom conveyor (56). Fiber is removed in a height direction from a longitudinal face of the fiber bed formed in filling chamber (13a) of fiber feeding device (19).