Stability of the Zr-Ni- Al bulk metallic glass (BMG) was investigated by making full use of its relevant crystals. The local atomic arrangements (characteristic atomic clusters) commonly existing in the BMG and its relevant crystals were identified by the experimentally determined radial distribution functions. We found that the local atomic arrangements of the BMG were characterized by the prism clusters with a transition element, Zr or Ni, in their center and the Kasper polyhedrons about an Al atom. Internal energy of these clusters was investigated by combinational use of the DVXα cluster calculation and the high-resolution photoemission spectroscopy. The prism clusters about the transition metal elements were confirmed to possess a low internal energy. We propose, as a consequence of present analyses, that the Zr-Ni-Al BMG is stabilized by the low internal-energy of the clusters and the large entropy caused by the freedom in the bond-direction between the clusters.