A Parametric Representation of Critical Curves and Caustics for a Binary Gravitational Lens

We find a simple expression for critical curves of a binary gravitational lens. On the basis of this, we present a parametric representation of such curves. The caustics can also be expressed with the same parameterization. The present result is helpful for efficiently constructing many templates of light curves due to binary systems, particularly extrasolar planets, which cause spikes in the light curves when a source crosses the caustics.