in the lower mechanism 4 that is the pulley 39 is fixed at approximately the center point of the arm shaft 31 rotational motion transferred to the pulley 39 is further transferred to the pulley 38 disposed in the bed 8 via the timing belt 41 a rotary hook shaft 37 is rotatably supported by a bearing 32 since the rotary hook shaft 37 is linked to the pulley 38 the rotary hook shaft 37 rotates in synchronization with the rotations of the arm shaft 31 due to the rotational motion of the pulley 38 the cantilever support 7 is formed on one end of the bed 8 the bed 8 supports a rotary hook 23 constituting a loop taker for catching a thread loop of the needle thread as the needle moves up and down and forming a stitch the lower mechanism 4 is provided inside the bed 8 for rotating the rotary hook 23 in synchonization with the reciprocal motion of the needle 16 the lower mechanism 4 comprises a rotary hook shaft 21 a helical gear 22 the rotary hook 23 a helical gear 24 and the rotary hook shaft 37 mounted on a metal lower frame 20 the lower frame 20 is mounted directly on the frame 1 by a plurality of screws next the operations of the lower mechanism 4 will be described the rotational motion transferred via the timing belt 41 to the pulley 38 is transferred to the helical gear 22 via the rotary hook shaft 37 rotatably supported by the bearing 32.