  The electronic structure of the $f$-based superconductor $\mathrm{CeIr_3}$
was studied by photoelectron spectroscopy. The energy distribution of the
$\mathrm{Ce}~4f$ states were revealed by the $\mathrm{Ce}~3d-4f$ resonant
photoelectron spectroscopy. The $\mathrm{Ce}~4f$ states were mostly distributed
in the vicinity of the Fermi energy, suggesting the itinerant character of the
$\mathrm{Ce}~4f$ states. The contribution of the $\mathrm{Ce}~4f$ states to the
density of states (DOS) at the Fermi energy was estimated to be nearly half of
that of the $\mathrm{Ir}~5d$ states, implying that the $\mathrm{Ce}~4f$ states
have a considerable contribution to the DOS at the Fermi energy. The
$\mathrm{Ce}~3d$ core-level and $\mathrm{Ce}~3d$ X-ray absorption spectra were
analyzed based on a single-impurity Anderson model. The number of the
$\mathrm{Ce}~4f$ states in the ground state was estimated to be $0.8-0.9$,
which is much larger than the values obtained in the previous studies (i.e.,
$0-0.4$).
