The invention discloses an automatic switching device of double power supplies. The device comprises a mounting plate, a motor, a transmission mechanism and two sliding blocks for controlling the twocircuit breakers to be alternately switched on/off, wherein the two sliding blocks are arranged at the two opposite sides of the mounting plate in a sliding manner. The transmission mechanism comprises a rotary table which is located between the two sliding blocks and driven by the motor to rotate. The rotary table is provided with two driving shafts used for pushing the two sliding blocks to moveand a self-locking shaft used for being alternately matched with the two sliding blocks to limit the sliding blocks, and the two driving shafts and the self-locking shaft are distributed in a triangular mode. The transmission mechanism further comprises a pressing plate, and the pressing plate is parallel to the rotary disc up and down and connected with the two driving shafts and the self-locking shaft. The pressing plate can limit the tops of the two driving shafts, so that the two driving shafts are evenly stressed up and down in the conversion process, thereby avoiding the deformation, and improving the working stability of the whole device. The two driving shafts and the self-locking shaft are distributed in a triangular mode to support the pressing plate, thereby guaranteeing that the whole transmission mechanism is stable and reliable in structure.