An agricultural device comprising a frame (2) which can be moved and driven on the soil by a walking user, and a rotary tool (3) mounted on the frame (2) with a horizontal axis of rotation a motor drive (4) is fitted on the frame (2), which motor drive (4) exhibits a vertical-axis drive shaft (40), which drive shaft (40) is connected to the rotary tool (3) via a transmission belt (5) ring-wound around a drive pulley (50) coaxially fitted on the drive shaft (40), a driven pulley (51) coaxially fitted on the rotary tool (3), and at least a pair of return pulleys (52) having a rotation axis which is perpendicular both to the pulley (50) of the drive shaft (40) and to the pulley (51) of the rotary tool (3), which pulleys (50, 51) deviate the route of the transmission belt (5) from a plane where it winds around the drive pulley (50) to a plane where it winds around the driven pulley (51) the return pulleys (52) are rotatingly coupled to a belt-stretching body (53), which is mounted on the frame (2) such as to be able to move between a non-active position, in which the transmission belt (5) is loose, and an active position in which the transmission belt (5) is tensioned.
