The invention relates to a transmission, in particular between a drive shaft and a wheel driving shaft of an engine, in particular of an automotive engine, such as a riding mower engine, whereby this transmission is of the belt-controlled variable-speed drive unit type (2) combined with a clutch device (7).This transmission is characterized in that it is equipped with at least one progressive-type clutch device (7), preferably friction-based, and comprises a control mechanism (20) that is common to clutch device(s) (7) and to the variable-speed drive unit (2), whereby this control mechanism (20), in a first step, acts on the clutch device (7) to pass from the disengaged position, so-called of zero speed, to the engaged position that corresponds to the minimum operational speed of the variable-speed drive unit (2), then, in a second step, acts on the speed variation mechanism (6) of the variable-speed drive unit (2) to regulate as desired the speed of the engine that is equipped with such a variable-speed drive unit (2).