The purpose of the present invention is to provide a ventilation system with which stable ventilation can be performed. This ventilation system includes: an air supply means which is capable of forcibly supplying air by means of a drive source; a recess which is recessed into the floor of a compost shed in which material to be composted is deposited; an air pipe having one end connected to the airsupply means and an opening at the other end connected to the recess; a blocking plate which is provided on an upper end of the recess and blocks most of the open side of the recess; and a vent whichcomprises the non-blocked region of the open side of the recess, which is the region not blocked by the blocking plate, said non-blocked region being disposed so as to be larger than the open area ofthe air pipe.