To provide a power plant which is capable of improving the drive efficiency and power generation efficiency when electric power is generated using power of the drive part thereof.In a power plant (1), an output shaft (3a) of an internal combustion engine (3) is connected to driven parts DW and DW, and a transmission (20) is connected between the output shaft (3a) of the engine (3) and the driven parts DW and DW, while one of first to third elements (31), (32), and (34) of a planetary gear train (30) is connected between the output shaft (3a) of the engine (3) and the transmission (20), another one of the first to third elements to the output portion (42) of the generator-motor (40), and the remaining one of the same to the driven parts DW and DW.