A stair structure comprising a plurality of L-profile shaped elements, - each L-profile shaped element being formed as a monolithic piece, - each L-profile shaped element being formed from a composite material, which contains fiber-based components and/or plastic-based components, and which is used as the starting material, - each L-profile shaped element includes a first leg and a second leg, wherein dimensions of the L-profile shaped element being length, width and thickness of the first leg and the second leg, - wherein joint parts are fitted to the edges in the thickness direction of the first leg and the second leg, the joint parts being to function in the same manner in the interior as well as exterior of the L-profile shaped element, regardless which way around the L-profile shaped element has been turned, - the joint parts being selected from a groove or tongue structure, - each L-profile shaped element being arranged to be joined from the thicknesswise end of at least one of the first leg and the second leg, which is at the same time the lengthwise face of the L-profile shaped element, to at least one other L-profile shaped element of the same type by means of the joint parts, characterized in that - the first leg and the second leg being arranged to have substantially the same thicknesses and to have substantially different widths, - each L-profile shaped element being turnable to a desired position such that a plurality of such L-profile shaped elements are adapted to be fitted in a predetermined positions alternately both ways around, the rise part of a step of said stair structure being formed by a said L-profile shaped element being joined from at least one thicknesswise end of a leg to at least one thicknesswise end of a leg of another said L-profile shaped element, the external surfaces of these two L-profile shaped elements being adjacent to each other so that the joint between these two elements is provided to the middle of the rise part. - each L-profile shaped element being formed as a monolithic piece, - each L-profile shaped element being formed from a composite material, which contains fiber-based components and/or plastic-based components, and which is used as the starting material, - each L-profile shaped element includes a first leg and a second leg, wherein dimensions of the L-profile shaped element being length, width and thickness of the first leg and the second leg, - wherein joint parts are fitted to the edges in the thickness direction of the first leg and the second leg, the joint parts being to function in the same manner in the interior as well as exterior of the L-profile shaped element, regardless which way around the L-profile shaped element has been turned, - the joint parts being selected from a groove or tongue structure, - each L-profile shaped element being arranged to be joined from the thicknesswise end of at least one of the first leg and the second leg, which is at the same time the lengthwise face of the L-profile shaped element, to at least one other L-profile shaped element of the same type by means of the joint parts, - the first leg and the second leg being arranged to have substantially the same thicknesses and to have substantially different widths, - each L-profile shaped element being turnable to a desired position such that a plurality of such L-profile shaped elements are adapted to be fitted in a predetermined positions alternately both ways around, the rise part of a step of said stair structure being formed by a said L-profile shaped element being joined from at least one thicknesswise end of a leg to at least one thicknesswise end of a leg of another said L-profile shaped element, the external surfaces of these two L-profile shaped elements being adjacent to each other so that the joint between these two elements is provided to the middle of the rise part.