NOVELTY - Mixed gas having methane and carbon dioxide, and water are supplied to a hydrate-producing container (10). Carbon dioxide is dissolved in water, and portion(s) of carbon dioxide is hydrated. The obtained hydrate is continuously ejected in slurry form, from container. Methane and carbon dioxide in mixed gas are isolated, by recovering methane-containing gas concentrated from gaseous phase (51). Thus, isolation of mixed gas is enabled.    USE - For separating mixed gas such as biogas of organic refuse and sludge.    ADVANTAGE - Methane gas and carbon dioxide are efficiently and quickly separated from a mixed gas. The mixed gas processing system is economical and has excellent thermal efficiency.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) mixed gas separating apparatus, which has hydrate producing tank (10) for producing hydrate by gas-liquid contact, and gas diffusion tank (20) for diffusing gas component in hydrated slurry extracted from hydrate producing container. The hydrate producing tank has gas introducing portion for introducing mixed gas, a gas discharge portion for ejecting purified gas, and a slurry discharge portion for continuously extracting hydrated slurry; and    (2) mixed gas processing system. At least a type of gas (G1) in the mixed gas containing two or more types of gas having different hydrate producing equilibrium, is preferentially hydrated by supplying the mixed gas and raw material water in hydrate producing apparatus (A1). The obtained hydrate is extracted from the apparatus (A1) in slurry form. The obtained slurry is decomposed and gas diffusion is performed. The purified gas in a state in which the gas (G1) is removed from the gaseous phase, is recovered. The processed gas free from the gas (G), and raw material water are separately supplied to another hydrate producing apparatus (A2), and the processed gas is hydrated. A different gas component is isolated from the mixed gas, by recovering as final gas hydrate. The cooling heat accompanying gas diffusion of initially produced gas hydrate is utilized for manufacture and storage of final gas hydrate.    DESCRIPTION OF DRAWING(S) - The figure shows the mixed gas separating apparatus. (Drawing includes non-English language text).    hydrate producing apparatus (10)    water circulation line (11)    stirrer (12)    gas diffusion tank (20)    gaseous phase (51)