A tilting vehicle including a chassis (2), a steering unit (3) mounted to said chassis (2), and including a steering mechanism (31) that has two spaced-apart handle grips (311) arranged along an imaginary auxiliary line (L), a power unit (4) mounted to said chassis (2), and disposed behind said steering unit (3), and an air cleaner unit (5) mounted in said chassis (2), said tilting vehicle being characterized in that: said steering unit (3) further includes a tilting mechanism (32) that is connected to said steering mechanism (31), and that has two upright linking bars (322), each of which has top and bottom end segments, an upper crossbar (321) which has opposite end segments respectively pivoted to said top end segments of said upright linking bars (322), and a lower crossbar (323) which is disposed under said upper crossbar (321), and which has opposite end segments respectively pivoted to said bottom end segments of said upright linking bars (322), and two front wheel mechanisms (33) that are connected to said upright linking bars (322) of said tilting mechanism (32), respectively; said power unit (4) includes an engine case (41), and a crankshaft (42) that extends transversely and rotatably through said engine case (41) along a rotational axis (R); and said air cleaner unit (5) is disposed in a predetermined zone (Z) bounded by a horizontal top plane (S1) that overlaps the auxiliary line (L), two upright side planes (S2) that respectively intersect said upright linking bars (322) and that extend along a front-rear direction, and a horizontal bottom plane (S4) that extends horizontally and that overlaps the rotational axis (R), and is disposed between said tilting mechanism (32) and an upright longitudinal plane (S3) that overlaps the rotational axis (R). The tilting vehicle as claimed in Claim 1, further characterized in that said air cleaner unit (5) includes a main body (51) that defines an inner space (510), and that is formed with an upward-facing inlet port (511) spatially communicated with said inner space (510), a cleaner medium (52) that is detachably disposed in said inner space (510), and an air inlet component (53) that is connected to said main body (51) at said inlet port (511) and that extends upwardly. The tilting vehicle as claimed in Claim 2, further characterized in that said air inlet component (53) of said air cleaner unit (5) has an air collecting tube (531) that is spatially communicated with said inlet port (511), and at least one intake tube (532) that is connected to said air collecting tube (531) and that is formed with a suction port (530). The tilting vehicle as claimed in Claim 3, further characterized in that said suction port (530) of said at least one intake tube (532) is open rearwardly. The tilting vehicle as claimed in any one of Claims 3 and 4, further characterized in that said suction port (530) of said at least one intake tube (532) is open in a direction that is inclined downwardly and rearwardly. The tilting vehicle as claimed in Claim 3, further characterized in that said air inlet component (53) of said air cleaner unit (5) has two intake tubes (532) that are connected to left and right sides of said air collecting tube (531), respectively. The tilting vehicle as claimed in any one of Claims 3 and 6, further characterized in that said suction port (530) of said at least one intake tube (532) is disposed above said lower crossbar (323) of said tilting mechanism (32). The tilting vehicle as claimed in any one of Claims 3 and 6, further characterized in that said suction port (530) of said at least one intake tube (532) is disposed substantially at the same height as said upper crossbar (321) of said tilting mechanism (32). The tilting vehicle as claimed in Claim 1, further characterized in that said front wheel mechanisms (33) define therebetween a passageway (H) that is spatially communicated with said air cleaner unit (5). The tilting vehicle as claimed in Claim 2, further characterized in that said power unit (4) further includes a cylinder (43) that is disposed in said engine case (41), said main body (51) of said air cleaner unit (5) being further formed with at least one exhaust port (512) that spatially intercommunicates with said inner space (510) of said main body (51) and said cylinder (43), and that is disposed above said cylinder (43).