A power unit of a saddle-type vehicle, including an internal combustion engine and a belt-type continuously variable transmission integrally configured and mounted on a saddle-type vehicle, the power unit comprising: a transmission case joined to a crankcase bearing a crankshaft, extending in a vehicle-width direction, of the internal combustion engine, the transmission case extending to a lateral side of a rear wheel of the vehicle; a transmission case cover made of a metal and covering a lateral side of the transmission case, with respect to the vehicle-width direction, to cooperate with the transmission case to define a belt chamber; a main stand pivotally supported by a lower part of the crankcase and swingable between an erection position at which the main stand erects to support the vehicle and a retraction position at which the main stand is made to lie along a lower surface of the transmission case, the main stand having an operation part extending transversely to the main stand and being adapted to be positioned on an outer lateral side of the transmission case cover with respect to the vehicle-width direction when the main stand is located at the retraction position; and a wind-guide duct cover that has a duct cover rear part in a rear side thereof, the duct cover rear part extending rearward beyond a position of the operation part taken when the main stand is retracted; wherein at least a part of the transmission case cover is exposed to outside in side view; characterised in that: the transmission case cover has an open cooling wind inlet formed at a front part thereof to introduce a cooling wind into the belt chamber; and the wind-guide duct cover covers at least a front part including the cooling wind inlet of the transmission case cover from the lateral side with respect to the vehicle-width direction, in a manner to introduce external air into the cooling wind inlet. a transmission case joined to a crankcase bearing a crankshaft, extending in a vehicle-width direction, of the internal combustion engine, the transmission case extending to a lateral side of a rear wheel of the vehicle; a transmission case cover made of a metal and covering a lateral side of the transmission case, with respect to the vehicle-width direction, to cooperate with the transmission case to define a belt chamber; a main stand pivotally supported by a lower part of the crankcase and swingable between an erection position at which the main stand erects to support the vehicle and a retraction position at which the main stand is made to lie along a lower surface of the transmission case, the main stand having an operation part extending transversely to the main stand and being adapted to be positioned on an outer lateral side of the transmission case cover with respect to the vehicle-width direction when the main stand is located at the retraction position; and a wind-guide duct cover that has a duct cover rear part in a rear side thereof, the duct cover rear part extending rearward beyond a position of the operation part taken when the main stand is retracted; wherein at least a part of the transmission case cover is exposed to outside in side view; characterised in that: the transmission case cover has an open cooling wind inlet formed at a front part thereof to introduce a cooling wind into the belt chamber; and the wind-guide duct cover covers at least a front part including the cooling wind inlet of the transmission case cover from the lateral side with respect to the vehicle-width direction, in a manner to introduce external air into the cooling wind inlet. the transmission case cover has an open cooling wind inlet formed at a front part thereof to introduce a cooling wind into the belt chamber; and the wind-guide duct cover covers at least a front part including the cooling wind inlet of the transmission case cover from the lateral side with respect to the vehicle-width direction, in a manner to introduce external air into the cooling wind inlet.