To provide a roof panel installing structure having strong installation strength for easily installing a bracket on a rafter.

A roof panel 1 formed by installing the rafter 6 on an under surface of a face material 5, is arranged above a horizontal roof beam 3a or a purlin 2 orthogonal to the rafter 6. The bracket 4 formed by downwardly projecting a vertical piece 8, is formed on an inclined piece 7 inclining at the same inclination as the rafter 6. A notch groove 11 extending in the horizontal direction from the eaves side side edge 8c, is formed on the vertical piece 8 of the bracket 4. An upper flange 14 of the roof beam 3a or the purlin 2 is fitted in the notch groove 11 of this bracket 4. An upper surface of the inclined piece 7 is allowed to abut on an under surface of the rafter 6. The inclined piece 7 abutting on the under surface of the rafter 6, is fixed to the rafter 6 by a fixture 9 driven in from a lower part of the inclined piece 7.