The invention relates to a needle swing device of seamer, which arranges one resistance device on the guide element that guides the sliding of needle support that swing left and right with the needle, wherein said resistance device comprises: a plunger element contacted with the sliding surface of needle support; a screw spring for pushing the plunger to the sliding surface; a small screw elementand a locking nut for adjusting the elasticity of screw spring; therefore, it can avoid over-limit motion of step motor in high-speed rotation.