The invention relates to a driving member for a timepiece movement, that comprises two superimposed coaxial barrels (1, 11) coupled in series, each barrel including a spring provided in a cylindrical housing rotatingly mounted on a common shaft (20). The respective housings (2, 12) of the barrels are positioned opposite each other and do not include a lid, said springs (7. 17) being separated only by a separation washer (26) or a gap. Preferably, the separation washer (26) is made of a sheet of an anti-friction material and extends between the respective outer drums (4, 14) of the barrel housings. This arrangement can be used for increasing the height (H) of the springs, and thereby the amount of energy and the power reserve of the watch for an identical global volume of the driving member, or for reducing the total height of the driving member. The number of parts is also reduced and the mounting is made easier. Such a driving member is particularly intended for watches with a high power reserve.