gate 44 an inverter circuit 45 a cpu 46 a driving circuit 47 and a motor 48 are connected in turn the rotational number of the motor 48 is controlled by the cpu the other input terminal of the or gate 44 is connected via the chattering prevention circuit 49 with a normal or ordinal operation switch 50 further the output terminal of the chattering prevention circuit 42 is connected via a solenoid driving circuit 51 to the rotary solenoid 38 and is connected to the other input terminal of the and gate 43b it is noted that the differential operation switch 41 and the normal or ordinal operation switch 50 are actuated by a pedal 52a and a pedal 52b of a foot switch 52 respectively as shown in fig3 in operation when normal operation is selected first of all the dial 19a is rotated by an angle corresponding to the desired feeding quantity this rotation is transmitted via the member 18 and the pivoting of the rod 16 and the arm 17 to the lower feed regulator 9 thereby rotating the lower feed regulator 9 against the spring 20 thus the feeding quantity of the lower feed dog 13 is adjusted next when the pointer 33a is coincided with.