Abstract: A method of and apparatus for effecting artificial respiration in synchronism with a patient's voluntary breathing. The apparatus is in the form of an external body ventilator with an assistor, and comprises a jacket, a suction pump, a suction pipe, a changeover device, a jaw movement detection device, and a changeover controlling device. The jacket has a rigid shell for surrounding the chest of a patient and forming an air-tight chamber between the chest and the rigid shell when the jacket is applied to the chest of the patient. The suction pipe is in fluid communication with the air-tight chamber of the jacket, and the changeover device is for effecting a changeover between releasing the air in the air-tight chamber through the suction pipe and into the atmosphere during voluntary respiration, and connecting the suction pipe to the suction pump during artificial respiration.