first and second relays 26 and 31 the selector switch 22 is connected to the adding point 14 by a movable contact 220 for supplying the output of the long period stop mode controller 21 i e the output of the first control unit 25 or the second control unit 30 to the adding point 14 and is connected to the output of the long period stop mode controller 21 by a fixed contact 221 and is connected to e g a ground 38 for setting the loom to a normal stop mode by a fixed contact 222 the operation mode controller 19 compares as mentioned above an actually detected tension by the tension detector 12 and the predetermined target tension and drives the driving circuit 15 depending on the deviation between the actually detected tension and the target tension during the loom 1 operation thereby controlling the rotation of the let off motor 16 accordingly the warp 2 is always let off by the rotation of the let off beam 3 so that the tension of the warp 2 always equals the target tension the operator previously switches the selector switch 22 to the fixed contact 222 for the normal stop mode for the normal operation so that the adding output from the selector switch 22 is always set to 0 v accordingly when the loom stops during the weaving operation the tension control signal alone is supplied to the adding point 14 from the operation mode controller 19 as a result the.