PURPOSE: To prevent bobbin therad brakag caused by shortage of a bobbin thread on the way of sewing by providing each separate storage means for storing seam informaiton for forming plural patterns, and the necessary bobbin thread quantity at every pattern, and displaying the necessary bobbin thread quantity of a selected pattern on a display menas.

CONSTITUTION: By operating a pattern selecting means 6, a pattern seam information storage means 7 is retrived and information of a designated pattern is stored and held in a selected pattern storage means 9, and for starting a sewing machine, pattern control data is read out by aligniing the timing with a vertical motion of a needle, and by driving X and Y directin driving motors 11, 12, a pattern seam is formed. Also, in the this case, by a bobbin thread necessary quantity artihmetic program storage means 17, the bobbin thread necessary quantity correcponding to target seam information determined and stored in advance, and the quantity of the bobbin thread required by an arithmetic expression of a correction coefficient being different by thcikness of cloth, the kind of cloth, the kind of a thread, deformation of a pattern, etc., are calculated. Subsequently, this calculated bobbin theread quantity is displayed on a display means 18, and by confirming the bobbin thread quantity of a bobbin, sewing is performed.