PURPOSE: To narrow the breadthwise width of a root part in a stitch to be formed rather than an interval between button holes by moving a cloth holding member to right and left at intervals shorter than the moving intervals of a button holding member to the button holding member which is alternatively moved to right and left at the central distance intervals of a pair of the right and left button holes.

CONSTITUTION: When a sewing operation start switch is turned ON after a button B and cloth W are set, button crimping feet 2 and 3 are moved to right and left for each stitch together with a pedestal 1 samely as a conventional button sewing device and a needle N alternatively falls down to button holes B1 and B2. Simultaneously, both crimping boards 10 and 11 are also horizontally moved to right and left for each stitch while being pressed downward by a button holding member 6 and the cloth W is moved. However, since the move is executed at the intervals shorter than the moving intervals of the button holding member 6, the breadthwise width of root parts S1a and S1b in a stitch S1 to be formed by this sewing operation, namely, an interval ts1 between right and left needle fall points in the cloth W is shorter than an interval tb between the button holes.