Power train and transmission casing

A power train comprising:

• a prime mover having a drive output shaft, the prime mover having a prime mover casing constituting an outline of the prime mover;
• a transmission casing that is disposed side by side with the prime mover casing in a lateral direction intersecting an axial direction of the drive output shaft and defines a transmission chamber;
• and
• a transmission including a transmission input shaft disposed in parallel with the drive output shaft, and a plurality of gear trains for shift stages of an always-meshing type that are disposed in the transmission chamber and shift and output power input to the transmission input shaft,
• wherein the transmission casing includes:
• a casing body that defines the transmission chamber;
• and
• an extension portion extending in the lateral direction from the casing body and fixed to the prime mover casing to define a housing chamber that houses a portion of the drive output shaft protruding from the prime mover casing in cooperation with the prime mover casing.