In electrical engineering we can use various analytical tools for the circuit analysis. One possible method is the analysis by means of signal flow graphs. Analysis of electronic circuits using the MB graph is in detail described in [2, 3]. There are derived MB models (graphs) of passive elements (R, L, C) and of known amplifier structures, too. However, there are not described the transformer models - the circuit element with mutual inductance (M). In this article will be derived a signal flow graph of the transformer, therefore.