The invention relates to a magnetic flowmeter. The magnetic flowmeter (8) for measuring the flow of a flowing medium having a measuring tube (1) with a cross section that changes along its length and preferably the cross section in the middle section of the measuring tube (1) is less than at the beginning and end of the measuring tube (1), preferably the cross section of the measuring tube (1) is rectangular in its middle section and wherein the housing (2) preferably has a circular cross section. The inlet section (5) of the measuring tube (1) is formed of two segments (5a and 5b), of which a first segment (5a), in terms of flow direction, has a cross section that increases in the direction of flow and a downstream adjoining second segment (5b) has a cross section that decreases in the direction of flow. Optionally, the outlet section (6) is similarly formed of two sections (6a, 6b).