This invention provides an improved variable cam phaser for an automobile engine equipped with a controller capable of enabling execution of a given phase angle varying command in a shortened response time. The variable cam phaser has two control rotors which are arranged coaxial with a camshaft and rotatable relative to each other under the influence of two electromagnetic actuators and driven by the crankshaft of the engine. The variable cam phaser also has a relative phase angle varying mechanism for varying the relative phase angle of the camshaft relative to the crankshaft. When the two electromagnetic actuators are simultaneously energized, the two control rotors are held mutually unrotatable. However, when the braking torque of one actuator is reduced, the control rotor associated with that actuator is rotated relative to the other control rotor to immediately start the execution of the command.