This paper presents small signal ac analysis of LLC current resonant converter. Equivalent source model that represents a switching element as an equivalent source having averaged current and voltage is employed and described in detail. From analysis, the transfer function of the switching frequency to the output voltage of the converter becomes a quadratic system. Resonant capacitor and inductor do not affect directly to the small signal characteristics. However they affect a dc gain and an internal resistance. The analysis method is confirmed by experiments, and experimental results are relatively consistent with the analytical results.