Slightly Cu-rich CuGaSe2 films were grown on  oriented GaAs substrates by molecular beam epitaxy. Photoluminescence of the films showed a remarkable emission peaked at 1.71 eV at low temperature, which is attributed to recombination of free excitons and bound excitons. The dissociation energy of free excitons and their localization energy to a center are found to be 16.2 and 3.3 meV, respectively. The band-gap energy Eg is estimated to be 1.7310 eV at low temperature. It is suggested that the temperature variation of Eg is dominated by interaction with phonons of 26 meV which corresponds to the mean energy of the optical phonons in CuGaSe2.