To provide a curtain rail device that can be installed freely in a curve form in accordance with the shape of the window sash without any need of a special mechanical facility when curving the curtain rail, can smoothly run through the runner, and is provided with good resistance against weight and durability.

The curtain rail device is equipped with: a strip-shaped curtain rail with an approximately rectangular cross section, made of aluminum extrusion with a lashing section protrudedly installed on outer surface, and keeping the outer surface in a convex shape to be able to form a curved shape; a multiple number of installing brackets that are placed and fixed at appropriate intervals on a frame surface or the window sash and hold the curtain rail in a curved form by being latched on the lashing section, a guide roller which turns around by being abut against the top end and the bottom end of the curtain rail, and a multiple number of runners that are provided with main bodies that pivot the guide roller from the inner side of the curtain rail, hang the curtain downward, and freely run through the curtain rail.