the stitch amplitude adjusting mechanism 24 and the work deeding mechanism 25 respectively thereby to form various patterns of stitches further the cpu 1 is responsive to pattern data from the program memory 10 to control the operation of a thread tension adjusting device 26 a pattern data memory 2 has pattern data stored therein which may be optionally selected by operation of a pattern selecting device 3 and may be modified by operation of a pattern data modifying device 4 with respect to the predetermined elements which form a single pattern fig2 and 3 show a composite pattern that is the pattern of french knots by way of example formed by the pattern data stored in the pattern memory 2 here the french knot pattern is composed of a series of patterns including two painted out elements 30 30 and the two straight line elements 31 31 located between the two painted out elements 30 30 the pattern data may be modified by the pattern data modifying device 4 for each of the painted out elements 30 30 and straight line elements 31 31 the pattern data stored in the pattern data memory 2 include the data for controlling the operation of thread tension adjusting device 26 in addition to the data for controlling the operation of the work feeding mechanism 25 and of the stitch amplitude adjusting mechanism 24 the pattern data may be modified regarding a plurality of predetermined elements to be stitched in a.