The patient, a 72-year-old man, was admitted for disuse syndrome after left lower thigh cellulites, who originally developed left hemiparesis at age 60. At the time of admission, he was alert, his Body Mass Index was 18.5 and his FIM (Functional Independence Measure) score was 49. We thought this was a case of post stroke disuse syndrome manifesting after long-term bedridden inactivity. He underwent a hospital rehabilitation program; however, he gained only poor functional recovery after one month. He complained about nighttime snoring and awakening from sleep. So he was evaluated with a portable device for SAS (Sleep Apnea Syndrome). His ESS (Epworth Sleepiness Scale) was 21, his Apnea-Hypnea Index was 58.2 and his lowest SpO₂ level was 75%. With a diagnosis of severe SAS, he was treated with nighttime nCPAP (nasal Continuous Positive Airway Pressure). After treatment, his lowest SpO₂ level rose to 90%, and the patient's excessive daytime sleepiness (ESS=15) and ADL (FIM=85) improved. When patients exhibit poor recovery after training, the possibility of SAS should be taken into consideration and they should be tested accordingly.