To securely avoid breakage of a missed weft in a tack-in apparatus by following up higher speed operation of a loom.

This control unit is constructed so as to enable motion transfer that converts rotations of a driving cam 5 into reciprocal motion of a holder rod 11 in weft direction by means of a spring 21 provided for a motion transfer system between the driving cam 5 that rotates synchronously with a loom and a capture cutting head 13 and to disable the spring 21 for a time with a stopper actuated by a weft inserting miss signal. In this construction the stopper actuated by a weft inserting error signal disables for a time the spring when a weft inserting miss occurs. As a result the rotations of the driving cam is not converted into the reciprocal motion of the holder rod in weft direction, and therefore the capture cutting head does not capture and cut the missed weft.