The gyroscopic power generator produces a high-speed rotation of magnets from low-frequency vibrations and supplies electric power to information and communication devices that use human vibrations in daily life. In this paper, in order to increase the stability and the output power of the generator, a simple equation that indicates the steady state approximate solution of phase difference is derived. From the derived solution, the phase difference of the precession angle is used as a margin factor of the stability. The control methods for the steady state and the transient state are then verified by the simulations. In an experiment to determine precession angle, a measurement method is developed in which the sensing coil is attached perpendicular to the generation coil and precession angle is obtained from the envelope of the coil voltage. In order to maintain the stability and high power generation for variable input vibrations, the impedance control method using the phase difference is developed and verified experimentally.