A power assist system for imparting additional force is arranged relative to a vehicle (e.g. a motor cycle) clutch mechanism (21) operating cable (16), and comprises an outer casing (36), inside which a reel member (44) on which the cable (16) is mounted, is in slidable contact with a rotor (38) rotatable about a motor (33) drive shaft (35). When an operating force is applied to the cable (16), a driving force from the motor (33) is applied to the cable (16) via frictional engagement of the reel (44) and the rotor (38). The reel member (44) may be split into segments (44a,44b,44c,44d). The motor (33) may be controlled by an ON-OFF switch (58) operatively connected with the cable (16).