  We study an inflationary scenario with a vector impurity. We show that the
universe undergoes anisotropic inflationary expansion due to a preferred
direction determined by the vector. Using the slow-roll approximation, we find
a formula to determine anisotropy of the inflationary universe. We discuss
possible observable predictions of this scenario. In particular, it is stressed
that primordial gravitational waves can be induced from curvature
perturbations. Hence, even in low scale inflation, a sizable amount of
primordial gravitational waves may be produced during inflation.
