PURPOSE: To eliminate occurrence of thread cutting at the time of contact, prevent drawing off the end of lower thread nipped by a thread cutting means, and have smooth and proper cutting of the lower thread by furnishing No.2 link member which makes restriction so that the revolving speed of No.1 arm becomes uneven by means of fitting of a detent pin at the base end of No.2 arm in a cam groove formed at one of the ends, and thereby lowering the revolving speed of the No.2 arm when the lower thread is in detention.

CONSTITUTION: A lower thread cutting under-cutter 1 is detained with a lower thread cutting over-cutter 2, a thread holding spring 3, and a shaft 1a, and they are arranged in the form of scissors to constitute a thread cutting means. No.2 arm 4 which contacts the lower thread to rotate it, is borne at the tip of No.1 arm 5 with the aid of a stepped screw 5a rotatably together with No.1 link member 6. The No.2 arm 4 draws out the lower thread from the bobbin while further rotating counterclockwise at a low speed. Meantime the lower thread cutting under-cutter 1, lower thread cutting over-cutter 2, and thread holding spring 3 rotate clockwise, and at last the detent part 2a of the lower thread cutting over-cutter 2 comes into contact with a stopper 8a. Thereby the lower thread is severed, and its end is held by the holding spring 3 and over-cutter 2.