the beginning b of the character b is cut the portion to be cut is stored in the memory 35 in operation when the needle 20 lowers into the end a of the character a as shown in fig1 the memory 35 sends a thread trimming signal to one terminal of the and circuit 25 connected to the drive circuit 23 the thread trimmer 78 operates when the needle 20 lowers into the fabric and the needle thread as well as the bobbin thread come between the movable knife 82 and the fixed knife 80 of the thread trimmer 78 therefore the other terminal of the and circuit 25 receives the timing signal from the phase detector 88 which indicates that the needle bar 22 is in its lowered position the and circuit 25 sends a drive signal to the drive circuit 23 on the condition that the and circuit 25 receives the thread trimming signal from the memory 35 and the timing signal from the phase detector 88 the drive circuit 23 drives the trimmer stepping motor 84 thereby operating the movable knife 82 of the thread trimmer 78 the needle thread as well as the bobbin thread are thus cut at the end a as shown in fig3 a similarly when the needle lowers into the beginning b of the character b the memory 35 sends the thread trimming signal to one terminal of the and circuit 25 the and circuit 25 sends the drive signal to the drive circuit 23 on the condition that the and circuit 25 receives the thread trimming signal from the memory 35 and the timing signal from the phase detector 88 the drive circuit 23 drives the trimmer stepping motor 84 to operate the.