  We constructed a new class of inflationary model with the higher derivative
axion field which obeys constant shift symmetry. In the usual axion (natural)
inflation, the axion decay constant is predicted to be in the super-Planckian
regime which is believed to be incompatible with an effective field theory
framework. With a novel mechanism originating from a higher derivative kinetic
gravity braiding (KGB) of an axion field we found that there exist a huge
parameter regime in our model where axion decay constant could be naturally
sub-Planckian. Thanks to the KGB which effectively reduces the Planck constant.
This effectively reduced Planck scale provides us the mechanism of further
lowering down the speed of an axion field rolling down its potential without
introducing super-Planckian axion decay constant. We also find that with that
wide range of parameter values, our model induces almost scale invariant power
spectrum as observed in CMB experiments.
