The invention relates to a shed forming device, comprising means provided to position warp yarns in order to form a shed in accordance with a pattern to be woven, before inserting a weft through this shed, the positioning of the warp yarns being the possible cause of an increase or a decrease of potential energy in the shed forming device, one or several elements being added, which may be able to compensate partly or entirely the decrease or increase of potential energy which is produced in the situation of the shed forming device, before adding the said elements to the shed forming device, and the said elements being incorporated in the shed forming device in such a manner, that the decrease or increase of potential energy will be performed by the said elements, in a manner independent of the positioning of the warp yarns. Furthermore the invention relates to a weaving machine comprising such a shed forming device.