  BICEP2 has observed a primordial gravitational wave corresponding to the
tensor-to-scalar ratio of 0.16. It seems to require a super-Planckian
inflationary model. In this paper, we propose a double hybrid inflation model,
where the inflaton potential dynamically changes with the evolution of the
inflaton fields. During the first phase of inflation over 7 e-folds, the power
spectrum can be almost constant by a large linear term in the hybrid potential,
which is responsible also for the large tensor-to-scalar ratio. In the second
phase of 50 e-folds, the dominant potential becomes dynamically changed to the
logarithmic form as in the ordinary supersymmetric hybrid inflation, which is
performed by the second inflaton field. In this model, the sub-Planckian field
values (~0.9 M_P) can still yield the correct cosmic observations with the
sufficient e-folds.
