In this paper, we propose an energy storage circuits for magnetic energy harvesting. We successfully harvested 104 mW from applied magnetic field of 90 μT at 60 Hz. This magnetic field is smaller than the value that ICNIRP2010 guideline provided. In order to use effectively the harvested energy, we consider energy storage circuits. Because an increase in an output voltage produced an increase in the storage energy, we use Cockcroft-Walton circuit for transform AC to DC voltage and step up voltage. Our proposed storage circuit consists of Cockcroft-Walton circuit, capacitor, and constant voltage circuit. It was found that the storage energy was proportional to the square of number of Cockcroft-Walton circuit steps. From experiments, we successfully demonstrate that our energy harvesting device can provide an energy of 1 J for magnetic flux density of 5.43 μT.