  We study effects of long-lived massive particles, which decay during the
big-bang nucleosynthesis (BBN) epoch, on the primordial abundances of light
elements. Compared to the previous studies, (i) the reaction rates of the
standard BBN reactions are updated, (ii) the most recent observational data of
light element abundances and cosmological parameters are used, (iii) the
effects of the interconversion of energetic nucleons at the time of inelastic
scatterings with background nuclei are considered, and (iv) the effects of the
hadronic shower induced by energetic high energy anti-nucleons are included. We
compare the theoretical predictions on the primordial abundances of light
elements with latest observational constraints, and derive upper bounds on
relic abundance of the decaying particle as a function of its lifetime. We also
apply our analysis to unstable gravitino, the superpartner of the graviton in
supersymmetric theories, and obtain constraints on the reheating temperature
after inflation.
