An apparatus for continuous adjustment of the working stroke of a driving machine, wherein the adjustment of the working stroke is simplified and rendered easier. A stroke adjustment spindle, mounted in a crank ring which is rigidly connected with a driven crank hub, in addition to manual operation, is further adjustable by an adjustment drive, preferably by a bevel gear drive, movable selectively in one or in the other opposite rotary adjustment direction. This adjustment is brought about by sitting the driving or control wheel of this double gear drive at one end of a control shaft, projecting axially through the driven crank hub and likewise driven with the latter, which control shaft is coupled for a joint drive at its counter end and is as well axially slidable on the latter. The control shaft receives an engaging element operable from the outside by means of an engaging lever arrested in the rest position and manually operable, which engaging element, depending upon the amount of the stroke adjustment, cooperates either with a coupling ring disc immovable in space, preferably on the side of the coupling housing, and disposed with an axial distance, for instance, on the left side from the engaging element, in the sense of a rotary locking of the double gear drive control shaft, or is provided with a second coupling ring disc disposed with an axial distance, for instance, on the right side from the engaging element, by means of an additional transmission drive driven from the crank hub with a peripheral speed higher than that of the crank hub in the sense of a bevel gear drive control shaft drive with its own driving speed surpassing the peripheral speed of the crank hub.