Provided are a flux-locked loop circuit, a flux-locked loop method and a superconducting quantum interference device (SQUID) measuring apparatus. The flux-locked loop circuit includes a pre-amplifier configured to amplify a signal output of a SQUID, an integrator configured to integrate a signal output from the pre-amplifier and output the integrated signal, an operating range expanding unit configured to initialize the integrator by comparing an output signal of the integrator with a positive or negative reference reset voltage corresponding to an external flux of a predetermined integral multiple of flux quantum, and a feedback circuit configured to supply current to eliminate a difference between the external flux applied to the SQUID and a magnetic flux corresponding to an integral multiple of the reference reset voltage according to the output signal of the integrator.