An actuating device for a sash of a sliding window or door, comprising: a carriage suitable for being associated to said sash, wherein said carriage comprises: - at least a slide provided with rolling means suitable for sliding along a substantially horizontal sliding direction corresponding to the sliding direction of said sash, - connecting means (104a, 104b) configured for mounting said slide on said sash so as to enable a secondary sliding motion (S1, S2) of said slide relative to said sash along the sliding direction, between a stationed position and a sliding position and vice versa, - at least a connecting portion suitable for being fixed to said sash, said connecting portion being operatively associated to said slide by means of inclined plane means (107, 108), so that the secondary sliding motion of the slide towards the sliding position determines a raising of the sash and the secondary sliding motion of the slide towards the stationed position determines a lowering of the sash, a rear command shaft suitable for being arranged along a rear head surface of said sash and operatively interposed between a rotating actuating member or handle of the actuation device and said carriage for generating said secondary sliding motion (S1, S2), a front command shaft suitable for being arranged along a front head surface of said sash and operatively interposed between said carriage and at least a retaining device of said sash for moving said retaining device between a closed position and an open position, wherein said rotating actuating member or handle is suitable for being mounted on said rear head surface of said sash having a rotation axis parallel to said sliding direction so that said actuating member or handle can rotate in a plane that is perpendicular to the sliding direction. a carriage suitable for being associated to said sash, wherein said carriage comprises: - at least a slide provided with rolling means suitable for sliding along a substantially horizontal sliding direction corresponding to the sliding direction of said sash, - connecting means (104a, 104b) configured for mounting said slide on said sash so as to enable a secondary sliding motion (S1, S2) of said slide relative to said sash along the sliding direction, between a stationed position and a sliding position and vice versa, - at least a connecting portion suitable for being fixed to said sash, said connecting portion being operatively associated to said slide by means of inclined plane means (107, 108), so that the secondary sliding motion of the slide towards the sliding position determines a raising of the sash and the secondary sliding motion of the slide towards the stationed position determines a lowering of the sash, a rear command shaft suitable for being arranged along a rear head surface of said sash and operatively interposed between a rotating actuating member or handle of the actuation device and said carriage for generating said secondary sliding motion (S1, S2), a front command shaft suitable for being arranged along a front head surface of said sash and operatively interposed between said carriage and at least a retaining device of said sash for moving said retaining device between a closed position and an open position, wherein said rotating actuating member or handle is suitable for being mounted on said rear head surface of said sash having a rotation axis parallel to said sliding direction so that said actuating member or handle can rotate in a plane that is perpendicular to the sliding direction. - at least a slide provided with rolling means suitable for sliding along a substantially horizontal sliding direction corresponding to the sliding direction of said sash, - connecting means (104a, 104b) configured for mounting said slide on said sash so as to enable a secondary sliding motion (S1, S2) of said slide relative to said sash along the sliding direction, between a stationed position and a sliding position and vice versa, - at least a connecting portion suitable for being fixed to said sash, said connecting portion being operatively associated to said slide by means of inclined plane means (107, 108), so that the secondary sliding motion of the slide towards the sliding position determines a raising of the sash and the secondary sliding motion of the slide towards the stationed position determines a lowering of the sash,