  We consider the effects on big bang nucleosynthesis (BBN) of the radiative
decay of a long-lived massive particle. If high-energy photons are emitted
after the BBN epoch ($t \sim 1 - 10^3$ sec), they may change the abundances of
the light elements through photodissociation processes, which may result in a
significant discrepancy between standard BBN and observation. Taking into
account recent observational and theoretical developments in this field, we
revise our previous study constraining the abundance of the
radiatively-decaying particles. In particular, on the theoretical side, it was
recently claimed that the non-thermal production of $^6$Li, which is caused by
the photodissociation of $\hefour$, most severely constrains the abundance of
the radiatively-decaying particle. We will see, however, it is premature to
emphasize the importance of the non-thermal production of $^6$Li because (i)
the theoretical computation of the $^6$Li abundance has large uncertainty due
to the lack of the precise understanding of the $^6$Li production cross
section, and (ii) the observational data of $^6$Li abundance has large errors.
