A 69-year-old man visited our hospital due to an abnormal shadow on a chest X-ray. Chest CT showed a mass shadow in his left lower lobe accompanied by an infiltrative shadow in the right upper lobe. Thorough examination led to a diagnosis of pulmonary squamous cell lung carcinoma, stage IIIB (T3N2M0). Combination treatment with chemotherapy and programmed cell death receptor 1 (PD-1) inhibitor was started, leading to a partial response. However, his pre-existing pulmonary infiltrative shadow progressed during the maintenance treatment with PD-1 inhibitor, and sputum culture revealed Mycobacterium abscessus infection. Thus, exacerbation of pre-existing nontuberculous mycobacterial pulmonary disease (NTM-PD) resulting from treatment with PD-1 inhibitor was suspected. Then, treatment with PD-1 inhibitor was discontinued, and he underwent pulmonary resection after antibiotic therapy against Mycobacterium abscessus infection. Recently, special attention has been paid to the association of Mycobacterium tuberculosis (TB) infection and treatment with immune checkpoint inhibitors (ICIs) in TB-endemic areas. This case also emphasizes the importance of realizing the risk of NTM infection when treating patients with ICIs, especially in NTM-endemic areas.