To provide a window automatic opening/closing system which controls opening/closing operation of a window by a sensor such as a rainwater sensor of a window (bay window) of a Western-style house, wherein the system is reliable and simple, and allows anyone to operate the same.

The bay window automatic opening/closing device is formed of: the bay window openably arranged in a bay window frame body via a pair of upper and lower links; a driving link arranged inside the bay window; a moving means for operating the driving link; and a link mechanism arranged between the window frame and the bay window, for determining an open front end location of the bay window. Thus automatic opening/closing operation and automatic locking/unlocking operation of the bay window can be achieved.