To provide a compact mechanism capable of easily adjusting a skew of a belt conveyor, in a bobbin treating device.

This bobbin treating device carries a yarn feeding bobbin by the belt conveyor. The belt conveyor has an endless annular flat belt, a motor 31, a motor bracket 34 and a skew adjusting member. The flat belt is extended between a driven roller and a driving roller 28. The motor 31 fixes the driving roller 28 to its rotation output shaft 31a. The motor 31 is installed on the motor bracket 34. The skew adjusting member can rotate around the axis of a skew adjusting shaft 40. The skew adjusting member is provided with an eccentric part 42 eccentric to the axis of the skew adjusting shaft 40. The motor bracket 34 is positioned by contacting with the outer periphery of the eccentric part 42.