The present invention relates to a life gas mask. The purpose of the present invention is to provide a life gas mask which enables a surplus according to supply of oxygen exceeding a collected amount of carbon dioxide to be naturally discharged to the outside by removing carbon dioxide from air exhaled by self-contained breathing of a user without a separate air inflow from the outside and supplementing oxygen gas, thereby converting the oxygen gas appropriately for breathing to reuse the converted oxygen gas such that a circulation passage of expiration and a discharge passage of reused air surplus are separated. The life gas mask is a gas mask including a respiration unit which maintains respiration and blocks inflow of an external gas, and a visual field unit which secures a clear view. The respiration unit includes a circulation supply unit which circulates the collected and removed carbon dioxide by collecting and removing carbon dioxide contained in expiration of the user; an oxygen supply unit which supplements oxygen in the air circulated through the circulation supply unit so that air is used for rebreathing; and a surplus discharge unit which discharges a surplus of the air for rebreathing according to oxygen supplement in the direction, wherein the discharge passage of surplus air according to supplement of oxygen exceeding the collected amount of carbon dioxide through a circulation process is separated from the circulation passage of expiration filtered and circulated to supplement oxygen to expiration and use oxygen-supplemented expiration as the air for rebreathing, and the surplus air in rebreathing air is naturally discharged to the outside.
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