There is provided a support module of a sleeve for a transmission line, which is inserted into a part of a plurality of accommodation spaces formed at a flexible sleeve for a transmission line to prevent the sleeve for a transmission line from being slack, including a flexible flat plate; a plurality of bases fixed to the flat plate so as to be arranged in a longitudinal direction of the flat plate; a plurality of slack-preventing blocks that is connected to the bases to be positioned at a top of the flat plate and prevents the flat plate from being slack by coming in contact with each other; and a plurality of bending-degree restricting blocks that is connected to the bases and the slack-preventing blocks to be positioned a bottom of the flat plate and restricts a bending degree of the flat plate by coming in contact with each other.