The invention concerns an adjusting device for adjusting the pitch angle of a rotor blade of a wind power installation including an adjusting motor for moving the rotor blade through the pitch angle, an actuating unit for actuating the adjusting motor with electric current, wherein the actuating unit is connected to an electric power supply network, and an emergency power supply device for supplying and actuating the adjusting motor with electric current in the event of a failure of the electric power supply network, wherein the emergency power supply device has an electric storage means for storing electric energy to provide the electric current for actuation of the adjusting motor and wherein the actuating unit is adapted to charge up the electric storage means of the emergency power supply device with electric energy.