PURPOSE: To reduce size and to improve a function by a method wherein during opening and closing of a window having a sash top part pivotally mounted on a fixed main frame disposed on an inclination roof, the moving means of an opening closing operation member is contained in a small housing situated at a main frame bottom.

CONSTITUTION: A sash is pivotally mounted on one side of a fixed main frame approximately in a rectangular shape is openable. The ends on one side of pivotal moving arms 2 and 3 are then pivotally mounted on a small operator housing 1 mounted on the bottom member of the main frame. The ends on the other side of the arms 2 and 3 are slidably and pivotally movably mounted on a sash bottom member through slide shoes 2a and 3a. When a lead screw 5 in the housing 1 is rotated by a handle 6 and a nut 4 is elevated, the arms 2 and 3 are pivotally moved through a link 7 and a window is opened or closed. Further, in this case, one end of a compression spring 8 serving as a balancing mechanism is pivotally mounted on the bottom member of the main frame, a bar member 9 mounted on the other end is pivotally mounted on the arms 2 and 3 and the weight of a window during opening and closing is offset. This constitution improves stability and reliability and reduces size.