The present invention relates to a frequency synthesizer using a frequency offset compensated synchronization. To this end, the present invention, a first frequency divider generating a first frequency divider which divides the crystal oscillator frequency is output from the crystal oscillator to the values ​​set in advance; A second frequency divider generating a second frequency divider which divides the local oscillator frequency that is output from the local oscillator to a value set in advance; A first frequency divider and a phase / frequency detector 2 detects the phase and frequency difference between the divided frequency; A charge pump for charging or charge pumping according to the output signal of the phase / frequency detector; Filtering the low-frequency band of the output signal of the charge pump to the loop filter for outputting a comparison signal; A voltage controlled oscillator and by controlling the voltage value according to the comparison signal of the loop filter to control the voltage controlled oscillator the output frequency from the local oscillator; It includes, characterized in that to compensate for the frequency offset of the local oscillator frequency by the frequency offset synchronization. According to the present invention, the sigma in the frequency synthesizer of the Fraction-N type-phase delta modulator noise and minute defense spur remove noise, while the reference frequency it is possible to increase enough not to affect the loop bandwidth to remove the delta modulator Sigma there is an effect to reduce the noise to improve the in-band characteristics.