The present invention provides a power generator which can obtain efficient power generation by changing magnetic force acting on electromotive coils. The power generator is provided with a first permanent magnet member 1, a second permanent magnet member 2, and an electromotive coil member 3 arranged concentrically to have a telescoping structure and is configured so that power generation in the electromotive coil member 3 is induced by rotating the first permanent magnet member 1 or/and the second permanent magnet member 2. In the power generator, the first and second permanent magnet members 1 and 2 cooperate with each other to change the magnetic force and, thus, to obtain efficient power generation.