A roof window has a locking device (1) for locking the sash (4) in open positions relative to the casing (3); a device for opening the sash including spring arms (2) extending at a right angle to the window casing (3) at least in the closed condition of the roof window, and the spring arms (2) support the window sash (4) on said casing (3) in the open position thereof, the spring arms (2) are operatively connected both to the casing (3) and the window sash (4) by pivot bearings (5, 6), and one of the pivot bearings (6) is disposed on a spring-operated slide (8) movable in a guide (7). The slide being lockable by the locking device (1) which is operatable by a handle (9, 9').