Flux distribution in some inner-coil type thin film cores is discussed and equivalent magnetic circuits for the distributed flux are derived based on the theory of distributed constant circuit. The equivalent circuit has a simple structure and can give accurate inductance of the cores. Validity of the equivalent circuit is demonstrated for the sandwich type YIG inductor which exhibits forty times the inductance as a similar air core inductor. The equivalent circuit turns out to be mare simplified expression in the cases where the in-plane magnetic path in the magnetic film is very long and very short.