Optical properties near the band edge of hexagonal boron nitride were studied at 8 K. The photoluminescence spectrum shows two series of bands, namely, sharp (S) and diffuse (D), which are also distinguished by their fast (0.6 ns) for S and slow (5 ns) for D radiative decay time. Each series is composed of four bands with large Stokes shifts that are attributed to self-trapped excitons by the strong exciton-phonon interaction. The respective four luminescence bands of the two series originate from the four free-exciton levels in which the doubly degenerated dark and bright exciton levels theoretically predicted are resolved with the Jahn-Teller distortion in the excited states.