Type 304 stainless steel samples were irradiated with MeV-energy H and He ions and deuterium concentrations were in-situ observed by a nuclear reaction analysis (NRA) under a condition of continuous plasma exposure. It was found that one type of trap was produced by the irradiation and its trapping energy was 0.28 eV. The trap production rates to displacement were 6.8x10-3 for He ion and 5.1x10-4 for H ion, respectively. The trap was annihilated at 489 K in H-irradiated sample.