Transfer mechanism (20) is provided for reciprocally transferring a bobbin grasping device (10), grasping a bobbin case (B) at the distal end of a chuck section (11), between a rotary hook (6) of a sewing machine and a bobbin stock section (8). First cam plate (31) is provided adjacent to one end for orienting the chuck section (11) toward the rotary hook (6) during the transfer, while a second cam plate (41) is provided adjacent to the other end for orienting the chuck section (11) toward the bobbin stock section (8) during the transfer. The cam plates (31, 41) are detachable from the transfer mechanism (20), and, in transportation of the machine, one of the cam plates is transported as an attachment to a main sewing table, while the other plate is transported as an attachment to an extension sewing table. The bobbin grasping device (10) includes a moving body section (13), chuck section (11), and a spring member (19) for normally biasing the chuck section toward a predetermined neutral position.