Abstract: A thread cutting device for a sewing machine includes a front pivot member and a rear pivot member which extend through an elongated cutting plate and an elongated swing plate that is disposed between the cutting plate and a base plate. A driving rod is mounted swingably on the base plate, and has an end that is received slidably within a transverse slide slot in the cutting plate. When the driving rod is swung by a driving unit, the cutting plate and the swing plate rotate to align a cutter of the cutting plate with a needle. Then, the cutting plate is guided to move toward the needle relative to the swing plate. Each of the front and rear pivot members includes an eccentric wheel element that is formed with a threaded hole and that is rotatable relative to the cutting plate and the swing plate, and a bolt that extends threadably through the threaded hole in the eccentric wheel element to engage a threaded hole in the base plate.