Efficiency of power electronics circuit in switching power supply and motor drive system is being improved by developing SiC and GaN semiconductor power devices. On the other hand, power losses of magnetic parts including transformer, reactor, and motor are relatively noticeable. To overcome the above problem, it is necessary to establish a quantitative analysis method for power losses of magnetic devices. This paper introduces three recent topics of loss analysis of magnetic devices based on equivalent circuit method. The first one is an analysis of eddy current loss of Mn-Zn ferrite taking account of microstructure, the second one is a magnetic circuit model incorporating a play model, the last one is eddy current analysis of permanent magnet motor based on electric- and magnetic-coupled network model.