A high energy jet shower suitable for detailed analysis was found in one of the emulsion chambers flown in 1956 as the “Emulsion Chamber Project”. The charged secondary particles of this jet were analysed in the usual way and especially the energy of π 0 -mesons was determined by making use of the cascade showers developed from the γ-rays decayed from these π 0 -mesons. The energy of incident particles was obtained by the use of usual median angle method, and was estimated to be 5×10 13 e V (γ c =165). Next, by making use of the fact that transverse momenta of points are constant and by analysing cascade showers developed from γ-rays produced by the decay of π 0 -mesons, the energy of secondary particles was estimated. It was thus found that the differential momentum spectrum obtained is of the form d P / P 3 . Also inelasticity coefficients K ', K '' and K in the definition of the Bristol group were estimated to be 0.15, 0.10 and 0.5 respectively. Further, the results of the present analysis were compare...