[Object] To provide a compact and low-power-consumption artificial respirator and an operation method therefor. [Solving Means] In an artificial respirator 100 according to an embodiment of the present invention, the control section 17 controls the valve mechanism 5, 8 to be driven, to thereby alternately switch between a first state for feeding inspiratory air stored in the reservoir tank 4 to a patient and a second state for releasing expired air of the patient. The pressurizing pump 1 has a discharge function for reversing a reduction of pressure within the reservoir tank 4, which is caused due to the inspiration, within an expiration period of time. Here, the expiration period of time (second period of time) is set to be equal to or longer than the inspiration period of time (first period of time), and hence a pressurizing pump having a small volume is allowed to supply needed inspiratory air into the reservoir tank 4. Thus, it is possible to reduce the volumes of the pressurizing pump 1 and the reservoir tank 4, and at the same time to achieve a reduction of driving electric power for the pressurizing pump 1.
