Method of manufacturing a security element which comprises a security element body having a window portion extending from a upper side to a lower side; formed of transparent material which merges into a window cantilever whose transparent material is completely non-transparently covered to the upper side and the lower side, comprising providing a core layer which is non-transparent at least in a surface portion, inserting a recess in the core layer within the non-transparent areal portion so that the recess is circumferentially enclosed by a non-transparent part of the areal portion, inserting transparent material into the recess; non-transparently covering a cantilever section of the recess to the upper side and to the lower side and introducing heat to form the security element body, characterized in that the insertion of the recess into the core layer and the filling with transparent material are each performed in multiple operations, and (a) first forming a first recess section comprising the window cantilever section and a part of the window portion (b) transparent material is inserted into the first recess section to fill the window boom portion and completely cover a boundary line between the window cantilever section and the window portion 25); and (c) the window cantilever section is covered at least to the upper side by an upper covering layer which is not transparent in the region of the window cantilever section and/or at the lower side by a lower covering layer which is not transparent in the region of the window cantilever section; and (d) the core layer, the filled transparent material and the upper covering layer and/or the lower covering layer are connected to each other in a punctiform manner and (e) subsequently widening the recess of the core layer so that the core layer is free of material in the window portion of the recess, wherein at the same time recesses are also made in the upper covering layer and/or the lower covering layer which are aligned with the window portion of the recess in the core layer, and (f) introducing transparent material for flush filling of the recesses. security element body having a window portion extending from a upper side to a lower side; formed of transparent material which merges into a window cantilever whose transparent material is completely non-transparently covered to the upper side and the lower side, comprising providing a core layer which is non-transparent at least in a surface portion, inserting a recess in the core layer within the non-transparent areal portion so that the recess is circumferentially enclosed by a non-transparent part of the areal portion, inserting transparent material into the recess; non-transparently covering a cantilever section of the recess to the upper side and to the lower side and introducing heat to form the security element body, characterized in that the insertion of the recess into the core layer and the filling with transparent material are each performed in multiple operations, and (a) first forming a first recess section comprising the window cantilever section and a part of the window portion (b) transparent material is inserted into the first recess section to fill the window boom portion and completely cover a boundary line between the window cantilever section and the window portion 25); and (c) the window cantilever section is covered at least to the upper side by an upper covering layer which is not transparent in the region of the window cantilever section and/or at the lower side by a lower covering layer which is not transparent in the region of the window cantilever section; and (d) the core layer, the filled transparent material and the upper covering layer and/or the lower covering layer are connected to each other in a punctiform manner and (e) subsequently widening the recess of the core layer so that the core layer is free of material in the window portion of the recess, wherein at the same time recesses are also made in the upper covering layer and/or the lower covering layer which are aligned with the window portion of the recess in the core layer, and (f) introducing transparent material for flush filling of the recesses. (a) first forming a first recess section comprising the window cantilever section and a part of the window portion (b) transparent material is inserted into the first recess section to fill the window boom portion and completely cover a boundary line between the window cantilever section and the window portion 25); and (c) the window cantilever section is covered at least to the upper side by an upper covering layer which is not transparent in the region of the window cantilever section and/or at the lower side by a lower covering layer which is not transparent in the region of the window cantilever section; and (d) the core layer, the filled transparent material and the upper covering layer and/or the lower covering layer are connected to each other in a punctiform manner and (e) subsequently widening the recess of the core layer so that the core layer is free of material in the window portion of the recess, wherein at the same time recesses are also made in the upper covering layer and/or the lower covering layer which are aligned with the window portion of the recess in the core layer, and (f) introducing transparent material for flush filling of the recesses.