PURPOSE: To smoothly operate a plurality of needle bars by the structure itself of the needle bar unit by forming a hole through which a shaft shaped section fixed to the other needle bar holder is slidably passed, in a slide member which is freely slid in a guide groove perpendicular to the needle bar held by the needle bar holder.

CONSTITUTION: A shaft shaped member 25 is fixed to the needle bar holder 24 of a needle bar 14 at its one end, and the other end of the member is extended toward the needle holder 25 of the other needle bar 2 in the direction perpendicular to the axial direction of each needle bar 2 and 14. An angular piece 27 is provided for a needle bar holder 23, which is freely slid in a slide groove 26 formed in the direction perpendicular to the needle bars 2 and 14 in the groove direction, and a hole is formed in the angular piece 27 through which the shaft shaped member 25 is slidably passed. When the one needle bar 2 is reciprocated by a crank 12 via the needle bar holder 23, the needle bars 2 and 14 are simultaneously reciprocated while being interlocked with the angular piece 27 and the shaft shaped member 25, and a needle bar stand 5 to which the two needle bars 2 and 14 are fixed, is thereby restrained from being deflected and curved, so that fine seams can be maintained, and needle can be prevented from being broken.