To provide a ventilator for auxiliary respiration and a safety valve of a patient conduit of an auxiliary respiration apparatus which enables safe and spontaneous breathing and prevents mixing of gases between inspiration and expiration without causing leakage.

To provide one safety valve 21 arranged in an assembly of a gas mixing conduit 7 and an inspiration conduit 8, a restrictor valve for excessive pressure, a valve which allows breathing from the atmospheric air and a direction valve for inspiration and coupled in a system. The safety valve is so arranged as to be controlled by an electronic control system 26 of a ventilator.