[Object] 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. [Solution] 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.