An experimental setup of an air shower array, hadron calorimeter, and emulsion chamber is being carried out at Mt. Chacaltaya (5200 m, Bolivia), in order to study the hadron interaction and the primary cosmic rays in the energy region exceeding 1015 eV. The number of hadrons in the air shower, detected by the hadron calorimeter, is discussed mainly in this paper. A comparison with the simulation shows that the number of hadrons in the air shower is not compatible with that of the simulation, indicating that the Feynman scaling law is violated more strongly than the one assumed in the simulation at 1016 eV. The average mass number of the primary cosmic rays, estimated from the distribution of the number of hadrons, is 〈lnA〉=2.8±0.5 at 1016 eV.