High-pressure X-ray diffraction experiments for selenium in a wide pressure range up to 150 GPa have been carried out and five structural phase transitions have been revealed: from hexagonal Se (Se-I) to an intermediate (Se-II) at 14 GPa, to base-centered monoclinic (Se-III) at 23 GPa, to base-centered orthorhombic (Se-IV) at 28 GPa, to β-Po type primitive rhombohedral (Se-V) at 60 GPa and further to body-centered cubic phase (Se-VI) at 140 GPa. The structural sequence corresponds to a change toward to higher symmetry and exhibits a similarity with that of Te.