A 39-year-old vegan man was admitted with diabetic ketoacidosis. He had also developed pneumonia that was unresponsive to antibiotics. Based on bronchoscopy findings, the diagnosis of Candida pneumonia was made, and the pulmonary shadow disappeared rapidly after antifungal therapy. Candida pneumonia has been mostly reported in severely immunocompromised patients. This is a rare case of Candida pneumonia that was found in a young vegan man with diabetes mellitus (DM). Although malnutrition caused by DM or an unbalanced diet is often underestimated as a cause of immunodeficiency, these conditions can be risk factors for serious opportunistic infections, including Candida pneumonia.