To suppress increase in temperature of a rotation output apparatus used for a loom and operated by passing electric current therethrough.

A yarn passage-changing body 23 for changing yarn passages of wefts Y1 and Y2 between a first yarn guide 17 and a second yarn guide 18 is driven by stepping motors 19A and 19B. These stepping motors 19A and 19B are each covered with covers 20A and 20B, and a radiating fin 28 is provided in covers 20A and 20B.