A filtering device for the air sucked in by an engine; said filtering device comprising: a parallelepiped-shaped air-box, which defines in its inside a cavity and presents two inlet openings towards the outside and two outlet openings towards a suction system of the engine; and two filters, each of which is housed inside the air-box, is arranged between an inlet opening and an outlet opening, and comprises in turn: a filtering material with tubular shape; a first end member, which closes a first end of the filtering material and presents a central through hole arranged in correspondence to the inlet opening, so as to allow the air to flow directly inside the filter; and a second end member, which closes a second end of filtering material opposite to the first end and presents no openings; the filtering device is characterised in that: said two inlet openings are obtained through two minor lateral walls of air-box, which are parallel and opposite to each other, so as to face each other and be coaxial; said two outlet openings are envisaged side by side through a same major lateral wall of air-box, which connects said two minor lateral walls to each other and is perpendicular to said minor lateral walls; and said two filters are arranged coaxial to each other, one after the other, and are centrally joined to each other in correspondence to said two second end members, which are rigidly connected to each other in an inseparable manner. a parallelepiped-shaped air-box, which defines in its inside a cavity and presents two inlet openings towards the outside and two outlet openings towards a suction system of the engine; and two filters, each of which is housed inside the air-box, is arranged between an inlet opening and an outlet opening, and comprises in turn: a filtering material with tubular shape; a first end member, which closes a first end of the filtering material and presents a central through hole arranged in correspondence to the inlet opening, so as to allow the air to flow directly inside the filter; and a second end member, which closes a second end of filtering material opposite to the first end and presents no openings; the filtering device is characterised in that: said two inlet openings are obtained through two minor lateral walls of air-box, which are parallel and opposite to each other, so as to face each other and be coaxial; said two outlet openings are envisaged side by side through a same major lateral wall of air-box, which connects said two minor lateral walls to each other and is perpendicular to said minor lateral walls; and said two filters are arranged coaxial to each other, one after the other, and are centrally joined to each other in correspondence to said two second end members, which are rigidly connected to each other in an inseparable manner. a filtering material with tubular shape; a first end member, which closes a first end of the filtering material and presents a central through hole arranged in correspondence to the inlet opening, so as to allow the air to flow directly inside the filter; and a second end member, which closes a second end of filtering material opposite to the first end and presents no openings; said two inlet openings are obtained through two minor lateral walls of air-box, which are parallel and opposite to each other, so as to face each other and be coaxial; said two outlet openings are envisaged side by side through a same major lateral wall of air-box, which connects said two minor lateral walls to each other and is perpendicular to said minor lateral walls; and said two filters are arranged coaxial to each other, one after the other, and are centrally joined to each other in correspondence to said two second end members, which are rigidly connected to each other in an inseparable manner.