A toy building element comprising one or more first beam-like parts (23, 24) with a plane internal face and an external face, and one or more other beam-like parts (21, 22) with a plane internal face and an external face. The beam-like parts are assembled in at least one corner whereby two internal faces are caused to form an angle of less than 180.degree. relative to each other. At least the first beam-like part (23, 24) is/are provided with an opening (7) that extends transversally thereto from the external face to the internal face, and the opening (7) is arranged so far towards the corner that the plane for the face of the plane internal face (4) of the second beam-like part (21, 22) intersects the opening in the plane for the face of the plane internal face (3) of the first beam-like part (23, 24). The plane internal face (4) of the second beam-like part (21, 22) is interrupted at a distance from the opening (7) whereby a clearance is provided around the opening (7) on the internal face of the first beam-like part.