An apparatus for controlling an LLC converter is provided. The apparatus includes a current controller that determines a first switching frequency control value of a switching element in the LLC converter to cause an output current detection value of the LLC converter to correspond to a predetermined output current command value. Additionally, a feedforward controller determines a second switching frequency control value for operating the switching element by applying a feedforward control value that corresponds to a ripple component included in an input voltage of the LLC converter to the first switching frequency control value.