An electromagnetic device and a high-voltage generating device which are thin and improved in the characteristics are provided in which a magnetic core 3 is made of a cylindrical form of a ferrite material having a higher intrinsic resistance. A winding is provided by winding a flat rectangular wire conductor 2 in an edge-wise winding form directly on substantially the entire length of the magnetic core 3. As any insulator such as a coil bobbin is not needed between the flat rectangular wire conductor 2 and the magnetic core 3, the winding can be decreased in the overall size or thickness thus contributing to the dimensional reduction of the electromagnetic device. Also, as its flat rectangular wire conductor 2 is wound directly on the magnetic core 3, the winding can be minimized in the length and thus the overall resistance. Moreover, as there is no gap between the winding and the magnetic core 3, the self-inductance can be reduced while the size and the number of turns of the winding remain unchanged.