50 in the rear of the base plate 40 another rigid shaft 62 extends longitudinally almost in the middle of the base plate 40 and is fixed on a pair of pedestals 63 via machine screws 64 since the rigid shaft 62 passes through shaft supporting members 66 and 67 of a second rocking member 65 the second rocking member 65 rocks around the rigid shaft 62 a shaft 68 parallel to the rigid shaft 62 is supported by a pair of supporting parts 69 of the second rocking member 65 a connecting member 70 for transmitting the movement of the first rocking member 53 to the second rocking member 65 is provided with three shaft supporting members 71 72 and 73 the shaft 55 passes through the shaft supporting member 71 and the shaft 68 through the shaft supporting member 73 the shaft supporting member 72 engages with the shaft 68 at a hole formed in its right side therefore when the first rocking member 53 rocks the connecting member 70 is driven back and forth and the second rocking member 65 rocks via the shaft 68 a rigid ring 74 is attached to the shaft 68 keeping in contact with the left side of the shaft supporting member 73 so as to prevent the connecting member 70 from moving laterally the feed dog 48 is fixed on a feed bar 75 via machine screws.