A device for mixing at least two fluid to pasty substances has a housing (2) with at least two openings (5, 6) for feeding the substances and with a discharge opening (8), a mixing element (3) which can rotate in the housing (2), which mixing element (3) can be displaced in the direction (17) of its axis (7) in relation to the housing (2) in order to adjust the size of a gap (18) between a conically tapering part (14) of the mixing element (3) and a likewise tapering region (15) of the housing (2) in order to adjust the shear rate in the region of the gap (18). The mixing element (3) has a region (9) in which annular ribs (11) are provided which project from the mixing element (3) and which engage between adjacent annular ribs (12) which project from the inner surface (10) of the housing (2).