PURPOSE: To shorten the standstill time of a splicing dolly and perform splicing and taking-up quickly and certainly by making the rotation of a friction roller identical to the yarn takeup speed when slack yarn does not exist in front of a sensor in the middle part of a slack tube, and putting the splicing dolly in traveling when it does not exist in front of a sensor at the foremost opening.

CONSTITUTION: When a slack yarn Y' does not exist in front of a sensor 38 in the middle part of a slack tube 36, the sensor 38 issues a signal to restitute an arm rod of an acceleration roller 31, and a ring-shaped drum and a motor are stopped rotating. Because a rotary shaft, meantime, continues rotating at the takeup speed, clutch between the rotary shaft and ring-shaped drum is engaged, and ring-shaped drum of a friction roller 20 is rotated associate with rotation of the rotary shaft. Thus the slack yarn Y' in the slack tube 36 will pass in front of another sensor 37 at the foremost opening. Because the slack yarn Y' will no more exist in front of this sensor 37, it is now practicable for a yarn splicing dolly 8 to move to the next operating position in conformity to the signal given by the sensor 37.