A magnetohydrodynamic device having a duct for a conducting gas to flow at an angle with the direction of the magnetic field induction vector. The duct is situated in the magnetic system and is provided with a plurality of electrodes adapted to interact electrically with the gas, whereas the cross-sectional shape of the duct working space is bounded by a closed contour formed by a curve inscribed into a rectangle having its sides a.gtoreq.b, while the minimum radius R of curvature of said curve is related to the distance x from the entry to the duct for the conducting gas to flow, to the cross-section under consideration by the following formula: ##EQU1## where P.sub.o and S.sub.o stand, respectively, for the perimeter and cross-sectional area of the duct 1 at the entry thereof, and 0.5.ltoreq..alpha..ltoreq.1.