A vacuum servo apparatus in which, in a performance diagram having an input coordinate axis perpendicular to an output coordinate axis, the normal operation is represented by a first operating line and, after a plunger member is moved by a solenoid so that movement of the plunger member with respect to a transmission member is controlled, the operation is represented by a second operating line following additional jump biasing force to be supplemented and generated is appropriately set and an output of the apparatus is designed to be faster during the return stroke for straightforwardly reflecting the intention of the driver.