A transformer, a method for manufacturing the same and an electromagnetic device are disclosed. The transformer includes a base plate, a magnetic core, transmission wire layers and conductive parts. The base plate includes a central part defining multiple inner via holes each running through the base plate and a peripheral part defining multiple outer via holes each running through the base plate. An annular accommodating groove is defined between the central pan and the peripheral part. The magnetic core is received in the accommodating groove. The transmission wire layers may be disposed respectively on two opposite sides of the base plate. Each of the transmission wire layers includes multiple wire patterns. Multiple conductive parts are respectively disposed in the inner via holes and the outer via holes.