Tegafur / gimeracil / oteracil potassium (TS-1) is widely used as a first-line drug for unresectable advanced gastric carcinoma and recurrent gastric carcinoma in Japan and the response rate of TS-1 against gastric carcinoma was reported to be excellent at 46.5% in a phase II study. However, since adverse drug reactions tend to occur in patients treated with standard regimen of TS-1, drug reduction or discontinuation is often required, which is one drawback of this drug. On the other hand, although Krestin (PSK) has been reported to show survival effects in postoperative immunochemotherapy against gastric carcinoma, the efficacy of PSK has not been established in patients with unresectable advanced gastric carcinoma and recurrent gastric carcinoma. Since the main effect of PSK was to recover physiological functions, including immune function of the host, it was expected that PSK would improve the compliance of TS-1 by alleviating adverse drug reactions of TS-1 therapy and the concomitant use of TS-1 with PSK would result in the improvement of treatment results. Therefore, we decided to conduct a randomized phase II study on patients with unresectable advanced gastric carcinoma and recurrent gastric carcinoma to compare TS-1 therapy with TS-1+PSK therapy.