To provide an inner window capable of obtaining an effective space for stably containing an object on the lower casing between the external window and the inner window as widely as possible.

The inner window 1 is provided to face the indoor side to a window casing B of the external window A provided to face the outdoor side, and constituted of the indoor window frame 2 and the inwardly opening type indoor screen 4. The indoor window frame 2 is framed so that at least the lower frame 12 of the upper frame 11, the lower frame 12, and both vertical frames 13, 13 is put through the lower frame against both vertical frames 13, 13.