Nivolumab, an anti-programmed cell death 1 antibody, has been approved for the treatment of unresectable advanced non-small-cell lung cancer (NSCLC). Although immune-related adverse events (irAEs) such as dermatologic, digestive, endocrine, hepatic, and pulmonary toxicities are known to occur upon administration of immune checkpoint inhibitors, case reports of polymyalgia rheumatica (PMR) associated with nivolumab use are rare. We report a case of an NSCLC patient who developed PMR during treatment with nivolumab and received corticosteroids. A 74-year-old man without a history of autoimmune diseases received nivolumab at a dosage of 3 mg/kg once every 2 weeks for the treatment of stage IIIB squamous cell carcinoma. After 12 cycles of nivolumab treatment, he developed grade 3 muscle pain and arthralgia, requiring hospitalization and discontinuation of nivolumab. A bone scintigraphy revealed no bone metastasis. Serological tests showed that although creatine phosphokinase did not increase, C-reactive protein and the erythrocyte sedimentation rate were both high. Tests for the rheumatoid factor, anti-cyclic citrullinated peptide antibody, and anti-nuclear antibody were negative. In addition to the serological findings, joint ultrasonography data and clinical symptoms were evaluated, leading to the diagnosis of PMR. Oral prednisolone 20 mg/d was started to treat the PMR without giant-cell arteritis. The patient's symptoms improved within 5 d of the initiation of treatment. Prednisolone was tapered to 5 mg/d without recurrence of PMR. Although grade 3 or 4 irAEs (except in type 1 diabetes) are generally treated with high-dose corticosteroids, grade 3 PMR associated with nivolumab use may be treatable with low-dose corticosteroids.