A magnetic element includes at least one primary winding, at least one secondary winding, a magnetic core, and an auxiliary winding. A winding segment or an entire of the primary winding or a winding segment or an entire of the secondary winding is defined as a parallel-connected winding set. The magnetic core includes a plurality of winding legs, two lateral legs, and two connection parts. The at least one primary winding and the at least one secondary winding are wound around each winding leg. The directions of magnetic fluxes through every two adjacent winding legs are opposite. The auxiliary winding is wound on one of two lateral legs, and electrically connected with the parallel-connected winding set. A direction of a magnetic flux generated by the auxiliary winding is opposite to a direction of the magnetic flux through the adjacent winding leg.