An electromagnetic device includes a substrate, magnetic cores, transmission line layers, and conductive members. The substrate is provided with annular receiving grooves for accommodating the magnetic cores; the substrate is divided into a central portion and a peripheral portion; inner and outer via holes are respectively formed on the central portion and the peripheral portion, respectively; the transmission line layers each including wire patterns are respectively provided on opposite sides of the substrate; and the conductive members are sequentially connected to the wire patterns on both sides of the substrate to form a transformer and/or a filter; the electromagnetic device has a first side provided with a slot and a second side parallel to the transmission line layers; and first conductive pins electrically connected to the at least one transmission line layers are provided on at least one of the side wall surrounding the slot and a second side.