To provide a window structure which makes it easy to open and close a skylight and generates on dead angle when a front upper window is opened by sliding it into the attic.

In the window structure of the cab of construction machinery, equipped with a skylight which can be opened and closed by rotating up and down and a front upper window which can be opened and closed by sliding along a guide rail installed on the front and the attic, the ceiling space is enlarged by protruding a cab ceiling backward, and a guide rail is extended to the enlarged ceiling space. The front upper window can slide backward to the position where the frame of the front upper window does not shut out an operator's visual field when the front upper window is opened.