Malignant melanomas easily metastasize and are often resistant to conventional classical therapies, i.e., surgery, chemotherapy and radiotherapy, in patients with advanced/metastatic malignant melanoma. In recent years, rapid advances have been made in the immunotherapy of malignant melanoma. New medicines, which have been approved by Federal Drug Administration (FDA), have dramatically improved the clinical outcomes for patients with advanced/metastatic melanoma. Nivolumab is an immune checkpoint inhibitor that targets programmed cell death-1 (PD-1) receptors. PD-1 is expressed on many immune cells, including T cells, B cells and natural killer cells. Engagement of PD-1 with its ligands (PD-L1 and PD-L2) induces functional exhaustion of the cytotoxic immune response. Nivolumab inhibits the PD-1 pathway, and thus activates the cytotoxic immune response. Although the immune checkpoint inhibitor tends to take a few months until it exhibits efficacy, once established, the efficacy often lasts for a long time. However, immune checkpoint inhibitors can have many adverse effects, including autoimmune-related inflammation. In particular, relevant severe adverse effects include interstitial pneumonia, colitis, liver dysfunction, thyroid disorders, and infusion reaction. Other affected organs include the skin, eyes, kidneys and nerves. Furthermore, several cases of fulminant type 1 diabetes mellitus have been reported in 2015 and 2016. Because we cannot predict what kinds of adverse effects will occur or when they will occur, we must observe patients carefully in order to detect any adverse events early on, and initiate appropriate treatments. The development of a number of new therapies will provide benefits for patients with malignant melanoma. Dermatologists must use these new drugs appropriately after determining the correct diagnostic information and providing supporting evidence.