To provide a beam mounting structure of a fence which can be easily installed by only one operator by improving construction performance.

A mounting bracket comprises a retainer bracket 3 for retaining the end of a fence beam 2, and a covering bracket 4 which covers the retainer bracket 3. In the retainer bracket 3, a retainer 32 which is opened obliquely upward from a vertical plate-like mounting portion 31 mounted to the front wall of a support 1 is longitudinally elongated. In the covering bracket 4, a covering portion 42 which is opened obliquely downward from a vertical plate-like mounting portion 41 mounted to the back wall of the support 1 is longitudinally elongated. The end of the fence beam 2 is retained by the retainer 32 of the retainer bracket 3, and the covering portion 42 of the covering bracket 4 covers the retainer from an obliquely-upward or horizontal direction. This enables the fence beam 2 to be temporarily placed on the retainer 32 in a state of fixing the retainer bracket 3 to the support 1. Thus, since one operator can perform not only the construction of the fence but also the operation of fixing the covering bracket 4 and the fence beam 2 by both his/her right and left hands, the efficiency of the operation can be dramatically enhanced.