A clock generator and an image sensor including the same are disclosed, which relate to technology for improving an operation speed of a voltage controlled oscillator. The clock generator includes a phase frequency detector (PFD) configured to detect a phase difference between a clock signal and a reference clock signal, a voltage converter configured to adjust a current corresponding to a voltage level in response to an output signal of the phase frequency detector (PFD), a filter circuit configured to generate a control voltage by filtering an output signal of the voltage converter, a voltage pumping circuit configured to pump an output voltage of the voltage converter, and provide the control voltage having a pumped voltage level, and a voltage controlled oscillator configured to generate a clock signal, an oscillation frequency of which is adjusted, in response to the control voltage.