A Coriolis mass flowmeter and a measuring tube unit for use in the Coriolis mass flowmeter with an inlet end and an outlet end, at least two measuring tubes and at least two transition pieces. In each case, one transition piece is arranged on a measuring tube at the inlet end. Each measuring tube has a measuring tube cross section and each transition piece has a transition piece cross section at the inlet. The transition piece is designed in one piece with the associated measuring tube, and the transition piece cross section deviates in its shape and size from the associated measuring tube cross section, the measuring tubes being arranged and aligned in such a manner that the transition piece cross sections form an overall cross section and thus a flow divider.