NOVELTY - Organic waste slurry including chlorine and/or chloride compound is formed by mixing organic waste containing livestock excretion and/or foodstuff waste material with water. The moisture content of the organic waste slurry is 60 mass% or more. The concentration of the solid content in the wastewater slurry is stirred by controlling the temperature of waste slurry which does not produce an anaerobic fermentation by sedimentation and retention of solid content of waste slurry. Thus, the organic waste slurry is stored.    USE - Storage of organic waste slurry.    ADVANTAGE - The method efficiently stores organic waste slurry, prevents solid content sedimentation of slurry and suppresses the dissolution of slurry. The biomass fuel is economical and has excellent combustion efficiency.    DETAILED DESCRIPTION - Organic waste slurry including chlorine and/or chloride compound is formed by mixing organic waste containing livestock excretion and/or foodstuff waste material with water. The moisture content of the organic waste slurry is 60 mass% or more. The chlorine containing organic waste water slurry with water equivalent amount of 10 times or more is the organic waste slurry. The concentration of the solid content in the wastewater slurry is stirred by controlling the temperature of waste slurry which does not produce an anaerobic fermentation by sedimentation and retention of solid content of waste slurry. Thus, the organic waste slurry is stored. INDEPENDENT CLAIMS are included for the following:    (1) storage apparatus (2), which contains storage tank which stores organic waste slurry, stirring unit which stirs the stored organic waste slurry and temperature control unit which controls the temperature of the stored slurry;    (2) fuel-formation method of organic waste slurry, which involves forming dechlorinated organic waste with a chlorine concentration of 3000 ppm or less by dehydrating and subjecting dechlorinated waste to drying or heat-drying process such that the moisture content is 35 mass% or more; and    (3) biomass fuel, which has heat generation amount of 3500 kcal/kg or more.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the storage apparatus.    Dissolution tank (1)    Storage apparatus (2)    Dehydrator (3)    Drying machine (5)    Grinder (6)