NOVELTY - The method comprises reacting organic matter with a microbial source in a reaction column to effect the decomposition and measure the weight of carbon dioxide produced, and decomposing cellulose with the above microbial source and measuring the weight of carbon dioxide produced as a reference value.    USE - The process is useful foe evaluating microbial-degradability of organic matter.    ADVANTAGE - The method comprises easy measurement procedures and is reliable. Also the process can be carried out by inexperienced operators and the apparatus is of simple structure which can be produced at low costs.    DETAILED DESCRIPTION - The method comprises:    (1) taking the organic matter as an evaluation subject together with a prescribed microbial source into a reaction column maintained constantly at a fixed temperature to effect decomposition of the organic matter in the reaction column using microorganisms contained in the prescribed microbial source under feeding of CO2-free saturated water vapor into the reaction column and to measure the weight of CO2 formed by the decomposition;    (2) and taking a cellulose as an evaluation reference together with the same prescribed microbial source into another reaction column maintained constantly with the same prescribed microbial source maintained constantly at the same fixed temperature to effect decomposition of the cellulose in the reaction column by the microorganisms in the microbial source under feeding of CO2-free saturated water vapor into the reaction column and to measure the weight of CO2 formed by the decomposition; and    (3) carrying out the comparative discussion of the two measured values to evaluate degradability of the organic matter.    An INDEPENDENT CLAIM is also included for the apparatus used for evaluating microbial-degradability of an organic matter comprising a reaction column maintained constantly at a fixed temperature and containing organic matter as an evaluation subject or a cellulose as an evaluation reference together with a prescribed microbial source. A means (comprising first CO2 adsorption means) for forming saturated water vapor is connected to one end of the reaction column and feeding CO2-free saturated water vapor into the reaction column and an adsorption column is connected to the other end of the reaction column containing a second CO2 adsorption means.    DESCRIPTION OF DRAWING(S) - The figure shows an explanatory view of the apparatus for evaluating microbial-degradability of organic matter.    Reaction column (1)    Organic matter (11)    Microbial source (13)    Means for feeding CO2-free saturated water vapor (21)    Means for forming saturated water vapor (23)    Second adsorption means (47)    Adsorption column (49).