To provide a bottom rail member capable of easily imparting a ventilation function to a sliding door, and the sliding door and a double sliding window which comprise the same.

A ventilation hole 13 is formed on a side plate portion 21 of a rail body 20 of a bottom rail member 1, and the ventilation hole 13 is opened/closed by an opening/closing portion 15. Thus, a ventilation function can be easily imparted to a sliding door in comparison with such a configuration that a ventilation device is separately attached to the sliding door. In addition, since the bottom rail member 1 is provided with a sash roller attachment portion 26, the ventilation function can be imparted to the sliding door concurrently with replacement of a sash roller 11 by replacing the sash roller together with the bottom rail member 1, for example, when the sash roller 11 is worn out.