Concealed screwing device for window frame including a latch unit and a buckle unit

A concealed screwing device for a window frame is disclosed. The concealed screwing device comprises a latch unit installed on a front window frame, and a buckle unit installed on a rear window frame. A lever that can be moved up and down is provided in the latch unit. The lever can drive a pair of bevel gear sets to rotate, and the bevel gear sets can drive a cam rotary latch to rotate and control a rotary buckle part of the cam rotary latch to hook or separate from a buckle of the buckle unit. The latch unit and the buckle unit are hidden in the window frame. Only a front surface of a lever base of the latch unit and the buckle of the buckle unit are exposed on the surface of the window frame, so as to maintain the overall appearance and aesthetics of the window frame.