An automatic clutch system includes an operating cylinder which is interconnected through a release lever with a friction element engaging mechanism. The operating cylinder is communicated with a master cylinder and an auxiliary cylinder through a hydraulic passage. A worm wheel driven by a motor has first and second connecting points which are oppositely disposed with respect to a rotation axis of the worm wheel. The first connecting point is interconnected with a piston rod of the master cylinder and has a first distance from the rotation axis. The second connecting point is interconnecting with a piston rod of the auxiliary cylinder and has a second distance from the rotation axis. The second distance is set smaller than the first distance so that the volume change of the auxiliary cylinder side is smaller than that of the mater cylinder side. Therefore, this cylinder arrangement functions stable to cancel a reaction force of a pressure spring of the friction element engaging mechanism to the worm wheel.