A power transmitting device provided with: a main input shaft (11) connected to an engine output shaft (2a) by a main clutch (CM); sub input shafts (12, 13) selectively connected to the main input shaft (11) by clutches (C1, C2); an output shaft (14) connected to the sub input shafts (12, 13) through a pair of gears (15, 16), respectively; and a power combining mechanism (9) configured so that a sun gear (9s) connected to the main input shaft (11), a ring gear (9r) connected to an electric motor (3), and a carrier (9c) connected to the first sub input shaft (12) can rotate differentially with respect to each other and transmitting combined power to the output shaft (14). The power of the engine and the power of the electric motor can be combined at high efficiency.