Cabin air treatment apparatus for an agricultural machine, comprising at least an external air inlet (11, 16), a filtration system (20), an HVAC system (30), and a cabin air supply outlet (40). The apparatus further comprises a hermetically closed box (1) inside which the HVAC system (30) is housed, the box having a levelling opening (60) for placing the box (1) into communication with a cabin (C) of the agricultural machine to level a pressure inside the box (1) with a pressure inside the cabin (C), wherein said at least one external air inlet comprises a first external air inlet (11) formed on the box (1). The filtration system comprises a first filter (21) for effecting a filtration of at least one among dust, aerosols and vapours, arranged at the first air inlet (11), and a blower (22) for drawing air from the first air inlet (11) and delivering it to the HVAC system (30), said blower being arranged directly connected downstream of the first filter (21) and inside the box (1).