Energy harvesting has become a highly important technology due to the development of portable electronic devices. In this study, we developed a rotary-type portable electromagnetic energy-harvesting device for
charging portable electronic devices from wind and water stream. The advantage of the developed device is that it does not use a mechanical shaft because it uses the magnetic axial coupling (magnetic force) between the
turbine and the device. In other words, the turbine can be easily replaced depending on the energy source. Furthermore, the device can produce the electrical power of mW class at a low rotating speed. The device consists of four inducing magnets, 16 pick-up coils, and a coupling magnet for combination between the device and the turbine. The device generated 35.15 V_rms at 300 rpm (5 Hz), and the maximum conversion efficiency reached up to 13.52 % at 240 rpm. We are aiming for energy conversion at a low rotational speed under 400 rpm and the device achieved mW class conversion: 360 rpm produced approximately 14 mW. To verify the proposed methods, we conduced various experimental analyses.