PURPOSE: To enable a pattern before sewing to be confirmed by causing the inching motion of a cloth presser device and a machine at every stitch, performing a calculation about the next shift direction from present, previous and next seam positions, and generating a warning and display, when the next shift direction deviates from the previous shift direction by the predetermined angle or more.

CONSTITUTION: Seam line data shown by displacement in X and Y directions at every stitch is saved in a floppy disk. When the present seam position is at (n) due to displacement as a result of inching operation, the cos θ of an angle θ formed with Δxn and Δyn and Δxn+1 and Δyn-1 is calculated, and compared with a constant value α. This value α is a maximum bend angle not generating a warning, and α=cosS. The bend angle θa of a seam (n + 1) next to the present seam (n) is less than S, and no warning is generated. In the case of a seam (n + 1)', however, a bend angle θb is larger than S, and a warning is generated. According to this system, a sewing machine is inched with a jog key, according to the seam data, and confirmation can be made before sewing as to whether the presser plate of a cloth presser device agrees to selected seam data.