Ventilator

A ventilator comprising:

• a pipe having a ventilation path;
• a relief valve;
• and
• a spontaneous-breathing valve;
• wherein the pipe includes
• a main port allowing a gas that is to be inhaled by a patient and a gas exhaled by the patient to pass through the main port,
• a relief valve port communicating with the main port through the ventilation path, and
• a spontaneous-breathing valve port communicating with the main port through the ventilation path,
• wherein the relief valve is mounted on the relief valve port and configured to be opened in accordance with a pressure in the ventilation path in such a manner as to be capable of allowing communication between the ventilation path and an outside of the pipe and releasing the pressure, and
• wherein the spontaneous-breathing valve is mounted on the spontaneous-breathing valve port, and the spontaneous-breathing valve is configured to be opened in accordance with an intake pressure at which the patient spontaneously breathes and configured to be capable of allowing communication between the ventilation path and the outside of the pipe and enabling inhalation.