[en] As for the major nuclides that compose SUS304 used in accelerator structures, this study searched the cross section of the (p, n) reaction using the EXFOR database. It was found that the cross section of the reaction exists even when the proton energy is less than 2.5 MeV, so it was confirmed that neutrons can be generated even in the low energy accelerator. From the main elements of SUS304, this study selected stable isotopes (Fe-57, Cr-53, Mn-55, Ni-64) having the cross section of (p, n) reaction, and calculated which element contributes to neutron generation, using the PHITS version 3.070. According to the calculation results, neutrons were generated, but the generated neutron flux was small. In the case of a small proton accelerator of 10 MeV or less, since the current value is low, the number of neutrons generated is small. In the case of 1.7 MV of tandem accelerator at Tokyo City University, it is not necessary to consider activation. However, comparison within this study alone is not enough, and it is necessary to calculate neutrons that contribute to concrete. (A.O.)