  Shift-symmetry is essential to protect the flatness of the potential, even
beyond the super-Planckian vacuum expectation value (VEV) for an inflaton
field. The breaking of the shift-symmetry can yield potentials suitable for
super-Planckian excursion of the inflaton. The aim of this paper is to
illustrate that it is indeed possible to break the shift-symmetry dynamically
within 4 dimensional supergravity prior to a long phase of inflation. Thanks to
the shift-symmetry, the leading contribu- tion to the inflaton potential is
free from the dangerous exponential factor even after its breaking, which is
the main obstacle to realizing the super-Planckian inflation in supergravity.
But, in our simple model, the resulting inflaton potential is a cosine type
potential rather than the power-law one and it is difficult to realize a
super-Planckian breaking scale unfortunately.
