To provide a method and an apparatus for manufacturing compost which effectively use agricultural waste, manufacture safe and high-quality compost within a short period of time at a low running cost and remove bad-smelling gas.

The method removes the bad-smelling gas and manufactures the high-quality compost by comprising a fermentation step wherein a fermenting substance containing effective microorganisms is added to the agricultural waste to decompose the waste and an exhaust-purification step wherein the bad-smell gas generated through the fermentation step is decomposed by photosynthetic bacteria under an anaerobic condition and carbon dioxide generated through the fermentation step is converted into oxygen by cyanobacteria. Furthermore, the compost can be manufactured at a low running cost.