To provide a wire fastening device capable of firmly fastening linear elements such as wire, and automating the fastening work.

The wire fastening device has a clip holding member 5 which holds a clip 10 while an opening part 10a of the clip 10 is directed in the arranging direction of wires 11, 12, and is reciprocally movable to the wires 11, 12, and a pair of clamping claws 7, 7 having bent recesses 21, 22 for bending the opening part 10a of the clip 10 along outer surfaces of the wires 11, 12, and clamping face parts 23, 24 for applying the clamping force to the clip 10 from the direction across the arranging direction of the wires 11, 12, reciprocally movable to the wires 11, 12, and openable/closable to each other. When the clip holding member 5 is moved, the clip 10 holds the wires 11, 12, and in this holding state, the clamping claws 7, 7 are closed to clamp the clip 10 from the direction across the arranging direction of the wires 11, 12.