The valence band dispersion of the graphite π band along the kz axis was measured using a sequence of photon energies between 60 and 230 eV. The interlayer interaction induces the well-known splitting of the π band into two, a lower binding energy band πL and a higher binding energy band πH. However, in the photoelectron spectra, the bands πL and πH appeared alternatively in the Brillouin zones along the kz direction. As a result, a 4π-periodic oscillation in the binding energy as a function of photon energy was observed for the π band dispersion. This is explained by considering the constructive and destructive interference of pz orbitals within the unit cell, called the photoelectron structure factor. We derived the analytic expression of the photoelectron structure factor for graphite. The resonance integrals of the pz orbitals were determined for the in-plane and interlayer. Furthermore, the inner potential of graphite from the vacuum level was determined to be 17.17 eV.