There is provided a power unit which makes it possible to attain the reduction of the size and manufacturing costs thereof, and improve turnability. The power unit 1 drives left and right driven parts WRL, WRR for propelling a transport machine V such that the transport machine is capable of travelling in a line and turning. The power unit 1 comprises a first energy input and output device 10 and a second energy input and output device 11 configured to be capable of inputting and outputting energy, and energy transmission devices PS1, PS2 provided between the first and the second energy input and output devices 10, 11, and the left and right driven parts WRL, WRR, for transmitting energy between the first energy input and output device 10 and the left and right driven parts WRL, WRR, and between the second energy input and output device 11 and the left and right driven parts WRL, WRR, wherein the first energy input and output device 10, the left driven part RL, the right driven part WRR, and the second energy input and output device 11 are in a collinear relationship in respect of rotational speed, and are in a line in this order in a collinear chart representing the collinear relationship.