A supporting device (100; 200; 300; 400) for a roller shutter winding tube in a roller shutter box, the supporting device being configured to cooperate with a respective end bearing or a motor bearing of the winding tube so as to maintain a longitudinal axis of the winding tube aligned with a main axis of the box in a use configuration of the supporting device, wherein the supporting device (100; 200; 300; 400) comprises: - a fixing plate (120; 420), which extends radially to a guide axis of the supporting device and in which is provided an indentation configured to cooperate with the corresponding end bearing or motor bearing in an assembled configuration, in which the guide axis is aligned with the longitudinal axis, and - at least one positioning member (150; 450), which is carried by the securing plate (120; 420) and which is movable relative to the securing plate between an adjustment configuration, in which the positioning member is adjustable in position relative to the securing plate, and a locked configuration, in which each positioning member is fixed relative to the securing plate and is configured to cooperate with an internal surface of the box so as to immobilise the fixing plate in the box in the use configuration, characterised in that: - the fixing plate also comprises a central drawer, in which the cavity is formed, and a peripheral portion, which carries the positioning member or members, - the central drawer is guided in translation relative to the peripheral portion along a drawer axis which is radial to the guide axis, and - the fixing plate also comprises an adjustment member, configured to adjust a position of the central drawer relative to the peripheral portion along the drawer axis. wherein the supporting device (100; 200; 300; 400) comprises: - a fixing plate (120; 420), which extends radially to a guide axis of the supporting device and in which is provided an indentation configured to cooperate with the corresponding end bearing or motor bearing in an assembled configuration, in which the guide axis is aligned with the longitudinal axis, and - at least one positioning member (150; 450), which is carried by the securing plate (120; 420) and which is movable relative to the securing plate between an adjustment configuration, in which the positioning member is adjustable in position relative to the securing plate, and a locked configuration, in which each positioning member is fixed relative to the securing plate and is configured to cooperate with an internal surface of the box so as to immobilise the fixing plate in the box in the use configuration, - a fixing plate (120; 420), which extends radially to a guide axis of the supporting device and in which is provided an indentation configured to cooperate with the corresponding end bearing or motor bearing in an assembled configuration, in which the guide axis is aligned with the longitudinal axis, and - at least one positioning member (150; 450), which is carried by the securing plate (120; 420) and which is movable relative to the securing plate between an adjustment configuration, in which the positioning member is adjustable in position relative to the securing plate, and a locked configuration, in which each positioning member is fixed relative to the securing plate and is configured to cooperate with an internal surface of the box so as to immobilise the fixing plate in the box in the use configuration, characterised in that: - the fixing plate also comprises a central drawer, in which the cavity is formed, and a peripheral portion, which carries the positioning member or members, - the central drawer is guided in translation relative to the peripheral portion along a drawer axis which is radial to the guide axis, and - the fixing plate also comprises an adjustment member, configured to adjust a position of the central drawer relative to the peripheral portion along the drawer axis. - the fixing plate also comprises a central drawer, in which the cavity is formed, and a peripheral portion, which carries the positioning member or members, - the central drawer is guided in translation relative to the peripheral portion along a drawer axis which is radial to the guide axis, and - the fixing plate also comprises an adjustment member, configured to adjust a position of the central drawer relative to the peripheral portion along the drawer axis.