Abstract: A feed dog device of a sewing machine includes a driving unit, a needle plate unit, a feed dog unit, an up-down transmitting unit, a horizontal transmitting unit and a direction adjusting unit. The direction adjusting unit includes a stepper motor with a variable rotational speed controlled in accordance with a speed of the driving shaft of the driving unit, and a linkage mechanism actuatable by the stepper motor to be moved to different positions so as to interfere with a horizontal reciprocating motion by the horizontal transmitting unit such that the horizontal reciprocating motion cooperates with the up-down reciprocating motion by the up-down transmitting unit to bring the feed dog unit into performing a variable moving course.