The present invention pertains to a method and an apparatus for treating municipal solid waste, and more particularly to a method and an apparatus for treating and recycling municipal solid waste not separately collected, and also for minimizing the amount of final waste to be buried. To this end, the present invention is characterized by comprising the steps of: an input step of inputting the municipal solid waste and microorganisms to a reactor; a first reaction step of firstly reacting the municipal solid waste with the microorganisms input to the reactor in the input step; a first separation step of transferring first intermediate matters completing the first reaction in the reactor to a first separator and then separating organic matters (it may also comprise small-sized inorganic matters passing through the screen of the first separator, also referred to as “second intermediate matters”) and inorganic matters, further comprising a recycled material recovering step of separating and recovering the recycled material by properties for recycling the inorganic matters; a second reaction step of transferring second intermediate matters passing through the first separator to a decomposing field constructed with good air circulation and then carrying out second reaction of the second intermediate matters; a second separation step of transferring third intermediate matters completing the second reaction in the decomposing field to a second separator and then separating foreign matters from the third intermediate matters; and a post-treatment step of post-treating fourth intermediate matters separated in the second separation step to make a final material.