To provide a control circuit of a current mode DC-DC converter, a current mode DC-DC converter and a control method thereof having excellent high-speed responsiveness with respect to fluctuations in output voltage. The control circuit of the current mode DC-DC converter serves as a DC-DC converter 1 that controls a peak value of a coil current and comprises a window comparator that detects whether an output voltage VOUT is within a predetermined voltage range including a target voltage, and a peak current setting unit that sets a peak current setting value of a coil current to a lower limit value or an upper limit value in response to a high or low voltage level of the output voltage VOUT, in the case that the output voltage VOUT is not within the predetermined voltage range including the target voltage.