To provide a hub unit and a wheel mounting structure, allowing easy mounting of a brake disc rotor and a tire wheel to a hub flange, and reducing manufacturing costs.

An outer periphery 17 functioning as a flange side guide part for supporting a brake disc rotor 50 and positioning the brake disc rotor 50 is formed on a hub flange 12. A rotor side guide part 68 of a tubular part 63 of the brake disc rotor 50 is brought into contact with the outer periphery 17, so as to determine an installation position of a brake rotor 50. A wheel spigot joint part 85 projecting on a vehicle inner side as a wheel side engaging part is formed on an inner peripheral side of the wheel disc part 81 of the tire wheel 80. An inner periphery 67 of an inner periphery mounting part 62 of the brake disc rotor 50 serves as the rotor side engaging part, so as to determine the installation position of the tire wheel by the wheel side engaging part and the rotor side engaging part.