The invention relates to a device for compacting a sliver (V) on a spinning machine. At least one rotatably supported nip roller (33) is associated with a compaction element downstream from a suction zone (Z) to form a nip line (P). The compaction element (17) and the nip roller (33) are rotatably supported on a shared support (20) that is detachably fastened to the spinning machine via fastening means (46). The compaction element (17) has at least one drive element (28) that forms a drive connection with a bottom roller (7) of a pair of delivery rollers (7, 8) via a weighting device (55, 58) when the compaction element is transferred from an idle position to an operating position. The support has a suction channel (SK) for the suction air of the compaction element (17). A first end (S1) of the suction channel (SK) is connected to the compaction element, and a second end (S2) of the suction channel (SK) ends in the area of the support (20), by means of which the support in its installed position is fastened to the spinning machine.