A bobbing case of rotating bobbing device for sewing machine capable of guiding bobbing thread and making it stably and continuously outgo from bobbing onto sewing area. The structure of bobbing casebody includes top face and side face, the side face can be divided into thick portion and thin portion by boundary portion, on the boundary portion, an outlet is set. Besides, it also includes an attachment equipped with a binding hole and a regulating hole, another end of the said attachment is equipped with first fixing piece and secondary fixing piece, in which the second fixing piece and supporting piece on the above-mentioned babbing case body side face are formed into a channel for leading-out bobbing thread.