A 61-year-old male was diagnosed with unresectable advanced gastric cancer(cT4b[SI; panc], N+, M0, cStage ⅣA). However he was administered S-1 plus oxaliplatin as a primary treatment and ramucirumab plus paclitaxel as a secondary treatment, the primary tumor and lymph nodes were enlarged. We judged PD and switched to the third-line treatment with nivolumab. After starting nivolumab, both the primary tumor and the lymph nodes shrank, and the PET-CT scan after 24 courses showed no FDG accumulation in the primary tumor or lymph nodes, so we judged the response as CR. The patient requested discontinuation of nivolumab, and nivolumab administration was stopped. Twenty months later after nivolumab administration was discontinued, CT scan showed re-growth of the primary tumor, and nivolumab administration was resumed. After resumption, he received 22 courses of nivolumab for 10 months with maintenance of SD.