Negative pressure pulmonary edema (NPPE) caused by airway obstruction was often life-threatening. Major cause of NPPE in adult patients was reported as post-operative laryngospasm. Therefore, NPPE was recognized widely among surgeons and anesthesiologist, but physicians also could face NPPE case in several clinical situation. NPPE in this case was caused by sleep apnea syndrome (SAS) as relatively rare cause. A 65-year-old female presented to emergency department due to disturbance of consciousness during sleep. This patient had desaturation requiring oxygen administration. Computed tomography showed pulmonary edema in bilateral lung fields. Comprehensive examination had no evident organic airway obstruction, and echocardiography showed normal cardiac function. This patient had been diagnosed with severe SAS with the apnea hypopnea index of 32 times/h. Therefore, we thought that the NPPE could be caused by severe SAS in this case. Continuous positive airway pressure therapy could improve this patient's symptoms promptly, and this patient could discharge without a complication. We should consider SAS as a cause of NPPE when examining NPPE patients especially with onset during sleep.