A condensing zone is arranged downstream of the front roller pair of a drafting arrangement of a spinning machine, in which condensing zone a drafted roving or a sliver is condensed. The condensing zone has a suction device which has a closed hollow profile and which serves as a sliding surface for a circulating sieve belt. The sieve belt transports the drafted fiber strand to a nipping roller, which presses the fiber strand and the sieve belt against the sliding surface at a nipping point. The fiber strand travels over an essentially in transport direction extending suction slit located in the condensing zone, which suction slit extends to the nipping point.