  We present the calculation of the atmospheric neutrino fluxes with an
interaction model named JAM, which is used in PHITS (Particle and Heavy-Ion
Transport code System). The JAM interaction model agrees with the HARP
experiment a little better than DPMJET-III. After some modifications, it
reproduces the muon flux below 1~GeV/c at balloon altitudes better than the
modified-DPMJET-III which we used for the calculation of atmospheric neutrino
flux in previous works. Some improvements in the calculation of atmospheric
neutrino flux are also reported.

High Energy Astrophysical Phenomena