To provide an aluminum sash with a key function that can lock the aluminum sash left slightly open to prevent theft by breaking a glass window or for ventilation regarding the aluminum sash of a building.

The aluminum sash with the key function is provided with: two rectangular recesses in parallel with a small space in non-openable positions of the window or lockable positions while ventilating at a lower frame of the aluminum sash of the double sliding glass window with a crescent lock. A lower side of each recess is provided with a movable piece so as to be vertically half-opened through a hinge, and an upper part of the movable piece is provided with hemispherical rubber not to open abruptly.