A cab air treatment apparatus for an agricultural machine includes an external air inlet, a filtration system, an air conditioning system, and a cab air supply outlet. The filtration system includes, in order: a first filter, a second filter, upstream of which is arranged a bypass valve for selectively putting the adsorption filter, or a bypass branch arranged in parallel with the second filter, in communication with the system, a blower for providing a desired pressurization downstream of the cab air supply outlet, and a deflecting valve having a main outlet connected to the air conditioning system, and a discharge outlet for cleaning the filtration system, said outlets being operable alternatively to one another.