A small power generating system includes a turbine driven by a fluid, a small high-speed rotation power generator including a permanent magnet rotor having a permanent magnet and rotated together with the turbine and a plurality of stator coils each of which is comprised of a coreless coil, the rotor being rotated such that voltage is induced on the stator coils, whereby power is generated by the power generator, and a back yoke disposed at one of two opposed sides of the stator coils which is opposed to the other side thereof further confronting the permanent magnet of the rotor, the back yoke being made of a magnetic material with a predetermined electrical resistance.