We present V, I CCD photometry of the Sextans dwarf spheroidal galaxy (dSph) in the Local Group. Images of the galaxy were taken by Suprime-Cam on Subaru, covering 26 fields extended to the tidal radius. The color-magnitude diagrams extending two magnitudes below the main-sequence turnoff (MSTO) show a steep red giant branch (RGB), blue and red horizontal branch (HB), blue stragglers, and main-sequence (MS) stars. From the luminosity difference between the HB and the MSTO, we estimate the ages of the galaxy's stellar populations. We find that the relatively younger stars (˜10Gyr) are more spatially concentrated toward the galaxy center than old stars (˜14Gyr), which indicates that the star formation in the central region continued at least a few Gyr. This is consistent with the different spatial distributions of red and blue HB stars. The long duration of the star-formation period in the central region of the galaxy is possibly related to dissipative gas physics during the epoch of post-reionization evolution, or to the accretion history of satellites.