Sewing machine

A sewing machine, comprising:

• a sewing needle, held by a needle bar and holding an upper thread to move reciprocally;
• an upper thread tension adjustment mechanism, adjusting a tension of the upper thread;
• a shuttle, holding a bobbin which is accommodated in a bobbin case and in which a lower thread is wound, and cooperating with the sewing needle to form a seam;
• a feed mechanism, in which endless feed belts feeding a sewing object disposed at a sewing position immediately below the sewing needle from the sewing position along a first direction are disposed on two sides with respect to the sewing position in a second direction orthogonal to the first direction, and in which a belt drive part is provided, the belt drive part independently driving the feed belt on a side and the feed belt on an other side with respect to the sewing position in the second direction;
• and
• a control part, controlling the upper thread tension adjustment mechanism, so that, from a beginning of sewing of the sewing object to an end of the sewing, a tension of the upper thread varies gradually in a variation amount in accordance with a difference between a feed amount of the feed belt disposed on the side with respect to the sewing position in the second direction and a feed amount of the feed belt disposed on the other side with respect to the sewing position in the second direction.