Lower thread supply device of sewing machine, and sewing method

A lower-thread supply device comprising:

• a bobbin case (300) including an outlet (330) from which lower thread is drawn out, and a needle through-hole (340) through which a needle (600) moving downwards with upper thread (a) being fitted passes;
• a hook body (200) in which the bobbin case (300) is mounted, the hook body being installed to be rotatable by a power device of a sewing machine, guiding upper thread (a2) on a sewn fabric side to a front area of the bobbin case (300) while catching and dragging the upper thread (a) via a hook (210), and guiding upper thread (a1) on a spool side to a rear area of the bobbin case (300);
• and
• a needle plate (800) formed above the needle through-hole (340) to be spaced apart from the needle through-hole (340) by a predetermined interval,
• wherein a needle hole (820) is formed in the needle plate (800) to be inclined towards the rear area of the bobbin case (300) in a direction from a front end to a rear end of the needle hole,
• wherein the bobbin case (300) is installed not to be rotated when the hook body (200) rotates, and
• the outlet (330) is formed in a position where the needle (600) may move downwards to a left of the lower thread (b) drawn out from the outlet (330), so that the upper thread is caught and dragged by the hook (210) on the left of a front of the lower thread (b) drawn out from the outlet (330).