A lower thread supply device of a sewing machine which is arranged below a needle plate of a sewing machine, comprising: a bobbin which has a cylindrical portion for inserting a spindle of a shuttle arranged below the needle plate, a shuttle side flange portion which is formed at an end portion at a shuttle side, which is a side facing the shuttle, of the cylindrical portion, and a front surface side flange portion which is magnetic and formed at an end portion at a front surface side, which is a side opposite to the side facing the shuttle, of the cylindrical portion, wherein 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; a bobbin case which has a non-magnetic cover portion housing the bobbin and transmitting a magnetic force, wherein the cover portion has a front surface side part covering the front surface side of the bobbin and a side wall part covering an outer circumference side of the bobbin; a magnetic force member which 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; and a magnetic force change portion which changes the magnetic force of the magnetic force member acting on the front surface side flange portion, the lower thread supply device being characterized in that the bobbin case further comprises a first lower thread supply resistance mechanism which gives a resistance action to the supply operation of the lower thread wound around the bobbin, in the form of a contact member arranged in contact with the bobbin on an inner surface of the bobbin case, the bobbin further comprises a taper portion inclined toward the shuttle side in an outer circumference portion of the front surface side flange portion, and the contact member arranged in the bobbin case is arranged in contact with the taper portion in a region facing the taper portion on an inner surface of the front surface side part. a bobbin which has a cylindrical portion for inserting a spindle of a shuttle arranged below the needle plate, a shuttle side flange portion which is formed at an end portion at a shuttle side, which is a side facing the shuttle, of the cylindrical portion, and a front surface side flange portion which is magnetic and formed at an end portion at a front surface side, which is a side opposite to the side facing the shuttle, of the cylindrical portion, wherein 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; a bobbin case which has a non-magnetic cover portion housing the bobbin and transmitting a magnetic force, wherein the cover portion has a front surface side part covering the front surface side of the bobbin and a side wall part covering an outer circumference side of the bobbin; a magnetic force member which 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; and a magnetic force change portion which changes the magnetic force of the magnetic force member acting on the front surface side flange portion, the lower thread supply device being characterized in that the bobbin case further comprises a first lower thread supply resistance mechanism which gives a resistance action to the supply operation of the lower thread wound around the bobbin, in the form of a contact member arranged in contact with the bobbin on an inner surface of the bobbin case, the bobbin further comprises a taper portion inclined toward the shuttle side in an outer circumference portion of the front surface side flange portion, and the contact member arranged in the bobbin case is arranged in contact with the taper portion in a region facing the taper portion on an inner surface of the front surface side part.