A roof window adapted for being installed in an inclined roof, said window comprising a window frame in which a top-hinged upper window sash and a bottom-hinged lower window sash are installed, said window frame comprising a top member, a bottom member, and at least two side members (2c, 2d), each window sash (3, 4) comprising a top member (3a, 4a), a bottom member (3b, 4b), and two side members (3c, 3d; 4c, 4d), said upper window sash being hinged adjacent to said window frame top member by means of at least one hinge mechanism, said lower window sash being hinged adjacent to said window frame bottom member by means of at least one hinge mechanism, each window sash (3, 4) being adapted for pivoting between at least one open balcony position and a closed position, said roof window further comprising two collapsible side railings, each side railing being connected to a window frame side member (2c, 2d) and a lower window sash side member (4c, 4d), said side railings being collapsed when said lower window sash is in said closed position and extended when said lower window sash is in said open balcony position (s), characterised in that said roof window comprises at least one electrically driven lower actuator, comprising an electric drive motor, arranged to pivot said lower window sash between said open balcony and closed positions, said lower actuator comprising a first actuator part and a second actuator part, said second actuator part cooperating with said first actuator part such that said lower window sash may be pivoted inwards towards a plane of said window frame and to said closed position, or may be pivoted outwards from said plane of said window frame towards said open balcony position, said first actuator part being fixed to said window frame side member(s) (2c, 2d), and said second actuator part being moveable either along said window frame side member(s) (2c, 2d) or in directions to and from said plane of said window frame, wherein, when said lower window sash is in said open balcony position, either both of said first and second actuator parts (10a, 10b) extend in parallel with said window frame side member (2c, 2d), or said first actuator part extends in parallel with said window frame side member (2c, 2d) and said second actuator part extends, in one of said directions from said plane towards an exterior of said roof window when said roof window is installed in an inclined roof, and said first and second actuator parts (10a, 10b) extending in parallel with said window frame side member (2c, 2d) when said lower window sash is in said closed position. a window frame in which a top-hinged upper window sash and a bottom-hinged lower window sash are installed, said window frame comprising a top member, a bottom member, and at least two side members (2c, 2d), each window sash (3, 4) comprising a top member (3a, 4a), a bottom member (3b, 4b), and two side members (3c, 3d; 4c, 4d), said upper window sash being hinged adjacent to said window frame top member by means of at least one hinge mechanism, said lower window sash being hinged adjacent to said window frame bottom member by means of at least one hinge mechanism, each window sash (3, 4) being adapted for pivoting between at least one open balcony position and a closed position, said roof window further comprising two collapsible side railings, each side railing being connected to a window frame side member (2c, 2d) and a lower window sash side member (4c, 4d), said side railings being collapsed when said lower window sash is in said closed position and extended when said lower window sash is in said open balcony position (s), characterised in that said roof window comprises at least one electrically driven lower actuator, comprising an electric drive motor, arranged to pivot said lower window sash between said open balcony and closed positions, said lower actuator comprising a first actuator part and a second actuator part, said second actuator part cooperating with said first actuator part such that said lower window sash may be pivoted inwards towards a plane of said window frame and to said closed position, or may be pivoted outwards from said plane of said window frame towards said open balcony position, said first actuator part being fixed to said window frame side member(s) (2c, 2d), and said second actuator part being moveable either along said window frame side member(s) (2c, 2d) or in directions to and from said plane of said window frame, wherein, when said lower window sash is in said open balcony position, either both of said first and second actuator parts (10a, 10b) extend in parallel with said window frame side member (2c, 2d), or said first actuator part extends in parallel with said window frame side member (2c, 2d) and said second actuator part extends, in one of said directions from said plane towards an exterior of said roof window when said roof window is installed in an inclined roof, and said first and second actuator parts (10a, 10b) extending in parallel with said window frame side member (2c, 2d) when said lower window sash is in said closed position.