A control circuit arranged to detect an initial rotor position of a brushless DC motor includes: a voltage integrator circuit, arranged to perform integration upon an input voltage, to generate a plurality of integrated voltages; a PWM generating circuit, arranged to generate and output a plurality of PWM signals to the brushless DC motor through a drive circuit, and stop outputting a PWM signal that is any of the plurality of PWM signals to the brushless DC motor according to an integrated voltage corresponding to the PWM signal; a current receiving circuit, arranged to receive a plurality of feedback currents from the brushless DC motor; a comparison circuit, arranged to perform comparison upon the plurality of feedback currents, to generate a comparison result; and a decision circuit, arranged to detect the initial rotor position according to the comparison result.