A reference-current optimizing apparatus of a Reference Junction Double Relaxation Oscillation SQUID (RJ-DROS) with a signal SQUID and a reference junction for detecting a magnetic flux signal is provided. The reference-current optimizing apparatus includes a voltage controller for converting a digital signal into an output voltage; a buffer for receiving the output voltage and preventing a current generated in the RJ-DROS from flowing inversely into the reference-current optimizing apparatus; a low-pass filter for eliminating a noise mixed in an output voltage of the buffer; and a resistor for converting an output voltage of the low-pass filter into a current and providing both ends of the reference junction with the current. The reference-current optimizing apparatus may also include a preamplifier having a number of junction bipolar transistors.