A drive-wheel axle unit which prevents the mutual contact portion between a caulk portion (29a) of a hub (6a) and an outer-end face (39) of a housing portion (11) of a drive shaft member (31) from being exhausted, thereby preventing the occurrence of shaky motion, strange sounds and vibrations for a long period of time. A flat surface (38) is formed in the end face of the caulk portion (29a), and is contacted over a large area with the outer end face (39), which makes it possible to reduce the contact surface pressure in the mutual contact portion between the flat surface (38) and outer end face (39).