Abstract: A lower thread supply device of a sewing machine includes a bobbin, a bobbin case, a magnetic force member, and a magnetic force change portion. The bobbin has a cylindrical portion for inserting into a spindle of a shuttle, a shuttle side flange portion, and a front surface side flange portion which is magnetic, and a lower thread is wound around an outer circumference of the cylindrical portion between the shuttle side flange portion and the front surface side flange portion. The bobbin case has a non-magnetic cover portion having a front surface side part and a side wall part, housing the bobbin and transmitting a magnetic force. The magnetic force member is arranged at the front surface side of the bobbin case and attracts the front surface side flange portion of the bobbin by a magnetic force via the bobbin case.

Abstract: A lower thread supply device of a sewing machine includes a bobbin, a bobbin case, a magnetic force member, and a magnetic force change portion. The bobbin has a cylindrical portion for inserting into a spindle of a shuttle, a shuttle side flange portion, and a front surface side flange portion which is magnetic, and a lower thread is wound around an outer circumference of the cylindrical portion between the shuttle side flange portion and the front surface side flange portion. The bobbin case has a non-magnetic cover portion having a front surface side part and a side wall part, housing the bobbin and transmitting a magnetic force. The magnetic force member is arranged at the front surface side of the bobbin case and attracts the front surface side flange portion of the bobbin by a magnetic force via the bobbin case.