Abstract: A driving force distribution/transmission device suppresses a shift of lubrication oil when a vehicle makes a turn, smoothly lubricates sliding parts, and improves reliability. The driving force distribution/transmission device 1 includes a gear input rotary member 53 and a gear output rotary member 55 that are interlocked to transmit a driving force through the meshing of a drive pinion gear 91 and a ring gear 93; and a left-right pair of clutch output adjusting mechanisms 57 and 59 coupled with both ends of the gear output rotary member 55, to carry out a driving force output adjustment through the engagement of frictional multiplate clutches 139. A closed and partitioned gear room 56 contains the drive pinion gear 91 and ring gear 93 therein. The main clutches 139 are contained in a left-right pair of closed and partitioned clutch rooms 125, respectively. Lubrication spaces in the three separate rooms, i.e.