Experimental study on tritium retention in tungsten was conducted, in which samples were irradiated with MeV-energy H or He ions and deuterium concentration profiles were subsequently observed under deuterium-plasma exposure conditions. The results showed that the deuterium concentration was significantly increased by irradiation at 573 K due to production of hydrogen traps while it was not under irradiation below 400 K. In the latter case, however, the concentration was increased when the sample was heated around 550 K. The trap was considered to be a kind of interstitial defects and grown at 550 - 600 K from irradiation defects. Once produced, the trap was stable at least 710 K.