NOVELTY - The present invention provides a method for generating electricity from gravitational force and magnetic force and an energy doubling device, which uses a small electric power input, going through gravitational force, magnetic power of a permanent magnet, magnetic power of electromagnet, and variation and movement of magnetic fields, to obtain double amount of electricity. This idea is similar to a high level financial management method, which uses various financial management means to invest a small amount of money and have a large amount of money in return. The invented device and method is intended to solve various crises, e.g. energy crisis, air pollution, etc. An iron block is fastened above a permanent magnet, and their clearance is adjusted by the attraction force of magnet so that the attraction force is larger than the gravitational force in order to enable the magnet to move rapidly and powerfully towards the iron block, thereby obtaining strong""magnetic attraction dynamic energy.""Next, the iron block is wound with coils and the coils are powered with an electric power to form an electromagnet. By altering the direction of electric current flow, the magnetic poles are altered into repulsive to enable the permanent magnet falling downwards to obtain strong repulsive force and gravitational force. By altering ON/OFF of electric power or using a Tai-Chi-type magnetic pole variation device to obtain alteration of direction of electric current flow, a repetitive up-and-down dynamic energy is obtained from the permanent magnet. This configuration can be made into a gravitational piston, which is applicable as mechanical energy on vehicles or boats to replace the driving power generated from fossil fuels, thereby overcoming the problems of air pollution and environmental issues. A smallest basic electric power input obtained by alternating magnetic poles is used to activate a permanent magnet and obtain strong attractive/repulsive forces. The gravitational force and a basic structure of magnetic field alternation and magnetic force cutting are used to assemble a permanent magnet, a balance device, and electric power generating coils into a multi-pole-type gravitational force magnet piston generator for obtaining required energy in order to drive machines, generation of electricity, or powering electrical appliances. Since the gravitational force is limitless, the invented device can be large or small and expandable according to demands. Also, the invention can be used to replicate unlimited amount of machines for replacing fossil fuel energy and reducing air pollution. If a magnetic repulsive force chain activation mode is used to produce 1:N chain activation, and a small-driving-large technology is used, a chain reaction similar to nuclear fusion is used to simultaneous produce a large amount of energy without the concern of radiation pollution, thereby endowing the invention with advantages over nuclear power generation.