A filtering device for filtering air, in particular for the cab of an agricultural machine operating with a system for spraying pesticides, the device comprises: - an outer housing, which defines an inner chamber and a fluid passage through the inner chamber; - a first filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of dust present in the air flow; - a second filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of aerosol present in the air flow; and - a third filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of vapour present in the air flow; wherein the second and third filter modules (6, 8) are arranged within the inner chamber and are permanently fixed to the outer housing so that they cannot be removed from the outer housing; and wherein the first filter module is arranged within the inner chamber and is coupled to the housing in a removable way, wherein the outer housing comprises a tubular body having a first end, coupled to which is a closing grill, and a second end, coupled to which is a connector for connection of the filtering device to an air-intake system of the agricultural machine, the inner chamber being delimited by the tubular body, the closing grill, and the connector, wherein the first filter module is surrounded by an annular gasket, by means of which it is snap-fit mounted on the first end of the tubular body, and wherein the closing grill is coupled to the first end of the tubular body via fast-connection means. the device comprises: - an outer housing, which defines an inner chamber and a fluid passage through the inner chamber; - a first filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of dust present in the air flow; - a second filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of aerosol present in the air flow; and - a third filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of vapour present in the air flow; - an outer housing, which defines an inner chamber and a fluid passage through the inner chamber; - a first filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of dust present in the air flow; - a second filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of aerosol present in the air flow; and - a third filter module for carrying out an action of filtering on a flow of air that traverses the fluid passage to eliminate or reduce the amount of vapour present in the air flow; wherein the second and third filter modules (6, 8) are arranged within the inner chamber and are permanently fixed to the outer housing so that they cannot be removed from the outer housing; and wherein the first filter module is arranged within the inner chamber and is coupled to the housing in a removable way, wherein the outer housing comprises a tubular body having a first end, coupled to which is a closing grill, and a second end, coupled to which is a connector for connection of the filtering device to an air-intake system of the agricultural machine, the inner chamber being delimited by the tubular body, the closing grill, and the connector, wherein the first filter module is surrounded by an annular gasket, by means of which it is snap-fit mounted on the first end of the tubular body, and wherein the closing grill is coupled to the first end of the tubular body via fast-connection means.