We theoretically study the electron transport in a proximity junction made by partially covering a graphene sheet with a bulk superconductor. Such a system serves as a normal conductor-superconductor (NS) junction and its electron transport properties are mainly governed by Andreev reflection (AR). In this NS junction, the charge neutrality point (CNP) of graphene must spatially vary as a result of the penetration of excess carriers induced from the superconductor. By taking this into account in the electron-doped case, we calculate the differential conductance G_(NS) of the graphene NS junction. Owing to the variation of the CNP in the uncovered region, a smooth pn junction is naturally formed at the point where the Fermi energy crosses the CNP. The resulting pn junction causes unusual behavior of G_(NS). For example, a resonant peak structure appears in G_(NS) reflecting the fact that quasi-bound states are created by the pn junction.
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