To provide an over-hang type unit building capable of effectively eliminating the deflection of an over-hang part by using a floor beam section of the standard specification for an upper-floor building unit.

In a unit building 1 comprising an upper-floor building unit 3 and a lower-floor building unit 2 assembled in a rectangular parallelepiped box formed of columns and beams, wherein the upper-floor building unit 3 installed on the lower-floor building unit 2 has an over-hang part 4 extended outward of the lower-floor building unit 2, a reinforcement beam 5 is added to a beam in the extending direction of the over-hang part 4 of the upper-floor building unit 3 or a ceiling beam in the extending direction of the over-hang part of the lower-floor building unit 2.