Disclosed is an adjusting circuit for determining a target delay clock signal of a delay circuit having a plurality of delay units. The delay circuit generates a plurality of delay clock signals, and the adjusting circuit includes: a difference signal generating circuit, for generating a plurality of difference signals according to a reference clock signal and the delay clock signals; a delay processing circuit, coupled to the difference signal generating circuit, for determining the target delay clock signal by computing a corresponding number of delay units for a specific phase of the reference clock signal according to the difference signals; wherein the target delay clock signal is one of the delay clock signals.