A 67-year-old Japanese woman was admitted to our Center complaining of general fatigue with a leukopenia value of 1600/μl. Chest high-resonance computed tomography revealed an initial involvement of interstitial pneumonia and she showed no dyspnea with the value of SaO₂ 96% in room air. We speculated Pneumocystis jiroveci pneumonia (PCP) and started combination therapy with methylprednisolone and antipneumocystis agent. In a few days, we noticed an elevated value of serum β-D-glucan＞300 pg/ml. It was strongly suggested that advocated corticosteroids as adjunctive therapy for PCP for patients with rheumatoid arthritis would give rise to significant effects on PCP in light of its poor prognosis. Further, the prophylaxis with antipneumocystis agents would be recommended to block person-to-person transmission of Pneumocystis jiroveci as the predominant route of acquisition.