To provide a connecting device of a sending-out warp beam hardly having variable factor such as backlash and the displacement of the center, and capable of accurate driving and transmitting.

This connecting beam has plural protrusions 18 protruding in the axis direction of a beam shaft 12, having tapered side surfaces narrowed in the tips, and formed on the circumference of a circle positioned in a face at the right angle to the axis direction, and a connecting member 20 to be driven, fixed to the end part of a beam shaft 12 of a sending out warp beam 1. Plural protrusions 22 protruding in the beam shaft 12 direction to direct to the connecting member 20 to be driven, and having tapered side surfaces narrowed in the tips are formed on the circumference of a circle positioned in the surface at the right angle to the shaft direction, and a connecting member 24 for driving is installed in a beam gear 14 so as to face to the connecting member 20 to be driven at a prescribed distance. A holding member 34 for fitting the protrusion 18 of the connecting member 20 to be driven with the protrusion 22 of the member 24 for driving so that the adjacent protrusions 18, 22 may be fitted to the facing protrusions 18, 22 without gaps, and keeping the state is installed therein.