A camshaft adjusting device for a motor vehicle has a stator and a rotor adjustable relative to the stator in a circumferential direction by a pressure medium. A restoring spring is arranged in a spring chamber and is configured to rotate the stator and the rotor relative to one another into an initial position when an engine of the motor vehicle is turned off. The restoring spring has a rotor end positive-lockingly connected to the rotor and a stator end positive-lockingly connected to the stator. One of the rotor end and the stator end is provided with a convexly curved embossment that cooperates with a convexly curved outer side of a positive-locking counter element on the rotor or stator, respectively. The embossment is provided at a radially outer end of the restoring spring. The restoring spring is a flat spiral spring.