A heretofore healthy 57-year-old man developed left back pain and high fever 1 day ago. Based on findings of his chest X-ray, pneumonia was diagnosed, and intravenous administrations of ceftriaxone and minocycline were begun by a primary care physician. However, he progressed to septic shock and acute respiratory distress syndrome within 12 hours after commencement of the above treatment, and he was transferred to our hospital. Chest CT demonstrated consolidation with cavitation in the left upper lobe and ground-glass opacity and consolidation in both lung fields. Treatment with mechanical ventilation and administrations of dopamine and noradrenaline were undertaken. A Gram stain of sputum detected numerous Gram-negative bacilli, and we then changed the antimicrobial regimen to a combination treatment with meropenem and ciprofloxacin, which resulted in an improvement of his systemic conditions. All cultures from sputum and blood culture grew Pseudomonas aeruginosa with the identical profiles of antibiotic resistance patterns. P. aeruginosa community-acquired pneumonia (CAP) in previously healthy individuals is very rare, although it progresses rapidly and exhibits high lethality. P. aeruginosa should be considered as pathogenic bacteria in critically ill patients with CAP.