A clip automatic-mounting tool comprises a clip holder (10) for holding and retaining a clip (C) to a first axial portion of a tensioning wire (W) embedded in a cushioned padding (P) for a seat, a drive cylinder (13) for moving the clip holder (10), a guide plate (11) including a portion having a first width substantially equal to that of the clip holder (10), and a tip end portion having a second width wider than the first width, the clip holder (10) being adapted to be moved along the guide plate (11) by the drive cylinder (13), and an insertion arm (12) extending along a side edge of the tip end portion of the guide plate (11) and forward protruding in an oblique upward direction from the tip end portion of the guide plate (11), the insertion arm (12) having a cutout groove (12b) formed in a tip end portion (12a) thereof for engagingly receiving a second axial portion of the wire (W), which is spaced from the first axial portion of the wire (W), when the insertion arm (12) is inserted into the cushioned padding (P).