The invention discloses an electromotor rotating automatically after starting and a generator rotating automatically after starting. The electromotor rotating automatically after starting consists of parts such as a small-sized direct-current electromotor and a small-sized direct-current generator (hereinafter referred to as electromotor and generator). Based on the principle of the difference of between different forces of a diesel engine, the reason for the automatic rotation can be shown by comparing two different forces of the combined electromotor rotor and generator rotor on a balance lever, and the diameter of the electromotor rotor, seen from a figure, is twice greater than the diameter of the generator rotor, so that the electromotor is specifically designed and is the key point. The electromotor rotating automatically after starting can be used on a working machine, a tricycle and a bicycle for supplying power. The principle of the generator rotating automatically after starting is the same as that of the electromotor rotating automatically after starting, and in configuration, the generator rotating automatically after starting is distinguished by that the electromotor power is one third of the generator power and that auxiliary parts are changed correspondingly. The generator rotating automatically after starting can be used by small-sized appliances.