We report a case of secondary adrenal insufficiency due to nivolumab. An 83-year-old man with acral lentiginous types of melanoma on the right sole visited our department in March 2017. He received primary surgery at referred hospital in June 2017, and pathological stage was IIIC (pT3bN3M0) according to AJCC (American Joint Committee on Cancer) 7th edition criteria. During the follow-up period, a lot of in-transit metastases appeared on the right leg. While we were resecting in-transit metastases, we concurrently started nivolumab in September 2018. After 17 cycles of nivolumab treatment, he developed severe nausea and anorexia. At baseline, his cortisol and adrenocorticotropic hormone levels were both at normal range, but corticotropin-releasing hormone loading test revealed secondary adrenal insufficiency. We diagnosed isolated adrenal insufficiency due to nivolumab. Treatment by hydrocortisone immediately relieved nausea and anorexia, and we could have continued treatment of nivolumab.