The present invention relates to an under-thread supply device for a sewing machine, and more particularly, to an enhanced under-thread supply device for a sewing machine, in which the device of the present invention and a unit for mounting said device are just partially changed so as to increase the winding amount of the under-thread of conventional sewing machines in order to achieve improved efficiency of sewing and efficiently reduce the puckering of a work piece without causing changes in the basic structure of conventional sewing machines.