We report on the intersection of spectral dependences of refractive indices n_o and n_e at the wavelengths 546 nm (λ ₀) and 450 nm (λ₀₁) in CdGa₂Se ₄ single crystals. The value of difference Δn=n _e-n_o is equal to zero at the wavelengths involved. When placed between two crossed polarizers, the crystals of CdGa₂Se ₄ exhibit a transmission band at the wavelength of λ₀=546 nm (300 K). The ground and excited states of three excitonic series (A, B and C) were found out at 13 K in CdGa₂Se ₄ crystals, and other parameters of excitons and bands were determined. In the λ point of Brillouin zone the effective mass of electrons m_c is equal to 0.14m₀, and the effective masses of holes m_v2 and m_v3 are equal to 0.76m₀ and 0.94m₀, respectively. The hole mass m_v1 depends upon the direction of wave vector k: at polarization E∥c, k∥a the mass m _v1=1.15m₀, and at polarization E∥c, k∥b m _v1=0.84m₀. The values of valence bands splitting in the center of Brillouin zone by the crystal field (Δ_cf=49 meV) and spin-orbital interaction (Δ_so=351 meV) were determined. The optical functions n, k, ε₁ and ε₂ in polarizations Eτc and E∥c for the energy diapason from 3 to 6 eV were calculated from the reflectivity spectra by Kramers-Kronig analysis. The evidenced features are discussed on the basis of recent theoretical calculations of the band structure of CdGa₂Se₄ crystals.