A slack preventing system comprising: a wire rod feeding machine that feeds a wire rod by rotating a spool around which the wire rod is wound; and a slack preventing device installed parallel to the wire rod feeding machine, characterised in that the slack preventing device includes: a reverse rotation roller having a rotating axis which is parallel to a rotating axis of the spool and rotating in a reverse direction to a rotating direction of the spool while being in contact with the spool; a forward rotation roller having a rotating axis which is parallel to a rotating axis of the reverse rotation roller and rotating in the same direction as the spool while being in contact with the reverse rotation roller; and a pinching roller having a rotating axis which is parallel to the rotating axis of the forward rotation roller and pinching the wire rod, which is fed out of the spool, together with the forward rotation roller; wherein the spool has: a columnar body portion around an outer periphery of which the wire rod is wound; and circular flange portions formed coaxially in both ends in an axial direction of the body portion, an outer periphery of the reverse rotation roller being in contact with outer peripheries of the circular flange portions, wherein an outer diameter of each of the circular flange portions is larger than an outer diameter of the wire rod which is wound around the winding drum portion of the spool so that an amount of the wire rod which is drawn on the basis of the rotation of the forward rotation roller becomes larger than an amount of the wire rod which is fed due to the rotation of the spool, and wherein an error which is generated between the feeding amount of the wire rod and the drawing amount of the wire rod is absorbed by a slip between the reverse rotation roller and the circular flange portion in the spool or a slip between the reverse rotation roller and the forward rotation roller. a wire rod feeding machine that feeds a wire rod by rotating a spool around which the wire rod is wound; and a slack preventing device installed parallel to the wire rod feeding machine, characterised in that the slack preventing device includes: a reverse rotation roller having a rotating axis which is parallel to a rotating axis of the spool and rotating in a reverse direction to a rotating direction of the spool while being in contact with the spool; a forward rotation roller having a rotating axis which is parallel to a rotating axis of the reverse rotation roller and rotating in the same direction as the spool while being in contact with the reverse rotation roller; and a pinching roller having a rotating axis which is parallel to the rotating axis of the forward rotation roller and pinching the wire rod, which is fed out of the spool, together with the forward rotation roller; wherein the spool has: a columnar body portion around an outer periphery of which the wire rod is wound; and circular flange portions formed coaxially in both ends in an axial direction of the body portion, an outer periphery of the reverse rotation roller being in contact with outer peripheries of the circular flange portions, a reverse rotation roller having a rotating axis which is parallel to a rotating axis of the spool and rotating in a reverse direction to a rotating direction of the spool while being in contact with the spool; a forward rotation roller having a rotating axis which is parallel to a rotating axis of the reverse rotation roller and rotating in the same direction as the spool while being in contact with the reverse rotation roller; and a pinching roller having a rotating axis which is parallel to the rotating axis of the forward rotation roller and pinching the wire rod, which is fed out of the spool, together with the forward rotation roller; wherein the spool has: a columnar body portion around an outer periphery of which the wire rod is wound; and circular flange portions formed coaxially in both ends in an axial direction of the body portion, an outer periphery of the reverse rotation roller being in contact with outer peripheries of the circular flange portions, a columnar body portion around an outer periphery of which the wire rod is wound; and circular flange portions formed coaxially in both ends in an axial direction of the body portion, an outer periphery of the reverse rotation roller being in contact with outer peripheries of the circular flange portions, wherein an outer diameter of each of the circular flange portions is larger than an outer diameter of the wire rod which is wound around the winding drum portion of the spool so that an amount of the wire rod which is drawn on the basis of the rotation of the forward rotation roller becomes larger than an amount of the wire rod which is fed due to the rotation of the spool, and wherein an error which is generated between the feeding amount of the wire rod and the drawing amount of the wire rod is absorbed by a slip between the reverse rotation roller and the circular flange portion in the spool or a slip between the reverse rotation roller and the forward rotation roller.