There are both advantages and disadvantages in the application of electromagnetic fields (EMF) for health: the former is deep brain stimulation for neurodegenerative disease in medicine and the latter is the possible association with a tumor. In this study, we examined the effect of EMF (50 Hz; 100 μT) on rat neural stem cells in vitro. During handling with culture cells, there are two phases of the state of neural stem cells isolated from rat brains; one phase is a cellular suspension in the medium (no anchorage), and another phase is anchorage to the bottom of the culture dishes. The effect of EMF on neural stem cells in vitro was dependent on these cellular phases. Upon anchorages, the cultured neural stem cells migrated along the radial axis, and exposure of these migratory neural stem cells to EMF (50 Hz; 100 μT) facilitates the migration and incorporation of BrdU 1.3~1.4 folds. However, these effects of EMF were not seen once the cellular suspension (no anchorage) was exposed. Even when the neural stem cells fully migrated, there were no effects of EMF on the retinoic acid-induced differentiation. Thus, there is a cell phase sensitive to EMF in the cultured neural stem cells.