An apparatus for compacting a continuous textile substrate by means of an elastic, endless belt, comprising: - a heatable rotating cylinder; - said endless belt movable along a closed path to support and transport the textile substrate in contact with a side surface portion of said heatable rotating cylinder, said belt being elastically deformable in elongation; - a roller system (31, 32, 33, 34, 35) on which said belt is wound in an elongation pretensioning state, wherein said roller system comprises a plurality of idle return rollers (33, 34, 35) and a plurality of motorized rollers (31, 32) operable so as to make said belt slide along said closed path imposing on said belt an additional elongation tension state at a first section of said path extending - with respect to an advancement direction of the belt - upstream of a second section of said path in which said belt is maintained in contact with the rotating cylinder; - means for guiding said textile substrate between said belt and said heatable cylinder along said second section of said path, wherein said roller system comprises a motorized drive roller, a motorized brake roller, a first idle return roller, which is arranged between said motorized drive roller and said motorized brake roller, and a second idle return roller, and wherein the first section of said path extends between said motorized brake roller and said motorized drive roller, passing in partial winding around said first idle return roller, while said second section of path extends between said motorized drive roller and said second idle return roller, wherein said closed path is completed by a third section extending between said second idle return roller and said motorized brake roller, in use along said third section of path said belt being in a relaxed tension state with respect to the first section of path characterized in that said second idle return roller is movable with respect to the other rollers (31, 32, 33) along an arc of circumference concentric to the rotation axis of the cylinder between a maximum winding position of the belt around said cylinder and a minimum winding position around said cylinder and is lockable in one or more intermediate positions between said two positions to adjust the extension of said second section of the closed path and in that said apparatus comprises a third idle return roller that engages said belt at said third section of the path and is movable with respect to the other rollers (31, 32, 33) to compensate for the position variations of said second idle return roller and thus maintain the pretension of said belt. - a heatable rotating cylinder; - said endless belt movable along a closed path to support and transport the textile substrate in contact with a side surface portion of said heatable rotating cylinder, said belt being elastically deformable in elongation; - a roller system (31, 32, 33, 34, 35) on which said belt is wound in an elongation pretensioning state, wherein said roller system comprises a plurality of idle return rollers (33, 34, 35) and a plurality of motorized rollers (31, 32) operable so as to make said belt slide along said closed path imposing on said belt an additional elongation tension state at a first section of said path extending - with respect to an advancement direction of the belt - upstream of a second section of said path in which said belt is maintained in contact with the rotating cylinder; - means for guiding said textile substrate between said belt and said heatable cylinder along said second section of said path, wherein said roller system comprises a motorized drive roller, a motorized brake roller, a first idle return roller, which is arranged between said motorized drive roller and said motorized brake roller, and a second idle return roller, and wherein the first section of said path extends between said motorized brake roller and said motorized drive roller, passing in partial winding around said first idle return roller, while said second section of path extends between said motorized drive roller and said second idle return roller, wherein said closed path is completed by a third section extending between said second idle return roller and said motorized brake roller, in use along said third section of path said belt being in a relaxed tension state with respect to the first section of path characterized in that said second idle return roller is movable with respect to the other rollers (31, 32, 33) along an arc of circumference concentric to the rotation axis of the cylinder between a maximum winding position of the belt around said cylinder and a minimum winding position around said cylinder and is lockable in one or more intermediate positions between said two positions to adjust the extension of said second section of the closed path and in that said apparatus comprises a third idle return roller that engages said belt at said third section of the path and is movable with respect to the other rollers (31, 32, 33) to compensate for the position variations of said second idle return roller and thus maintain the pretension of said belt.