PURPOSE: To improve workability and ensure the high fixed strength of a rail by enabling the rail to be fixed to a rafter, regardless of accuracy in a rafter gap in a right and left direction.

CONSTITUTION: In a fixing device for a rail 3 in the roof structure comprising a roof material such a roof tile 4, the rail 3 supported on a metal rafter 2 in parallel to an eaves, while the metal rafter 2 being so fixed to a base material 1 as to be orthogonal with the rail 3, an insertion section 12 is formed at one of vertical ends of the rail 3, and a clamp fixing section 13 at the other end. On the other hand, a pair of holding sections comprising an approximately inverted L-type lap section 10 allowing the coupling of the insertion section 12 of the rail 3 and a clamp piece 11 so erected as to correspond to the clamp fixing section 13, are formed on top of the metal rafter 2 in such a way as corresponding to the effective working breadth of the roof material. With the rail insertion section 12 coupled to the lap section 1 of the metal rafter 2, the clamp piece 11 is deformed to hold the clamp fixing section 13, thereby fixing the rail 3 to the rafter 2.