An HMT apparatus ( T ) is mounted on a vehicle ( A ). In the HMT apparatus ( T ), input rotational force from an engine ( 13 ) is once divided into two systems which are then transmitted by an MT device ( 23 ) and by an HST device ( 24 ) respectively and are re-synthesized for transfer toward wheels ( 12 ) and ( 16 ). The HMT apparatus ( T ) is disposed on the vehicle-body right side of the engine ( 13 ) which is sideways-mounted on a vehicle body ( 1 ), and its input and output shafts ( 25 ) and ( 26 ) are disposed in parallel with a crank shaft ( 13a ) of the engine ( 13 ) and are disposed to run parallel with each other. The input shaft ( 25 ) is coupled directly to the crank shaft ( 13a ) and an input gear ( 27 ) of the MT device ( 23 ) is mounted on the input shaft ( 25 ), and a hydraulic piston pump ( 30 ) of the HST device ( 24 ) is connected to the right side end of the input shaft ( 25 ). A planetary gear mechanism ( 28 ) of the MT device ( 23 ) is connected to the right side end of the output shaft ( 26 ), and a hydraulic piston motor ( 31 ) of the HST device ( 24 ) is connected to the right side of the planetary gear mechanism ( 28 ). By virtue of such arrangement, it is possible to improve the degree of freedom of the layout of each component of the HMT apparatus ( T ), to reduce axial dimensions, and further to provide improvement in the cooling property and maintenance property of the section of the HST device ( 24 ). The casing ( 81 ) of the HST is a separate structure of the HMT casing ( 80 ) and this makes it possible to easily remove it from the HMT apparatus ( T ).