A movable sinker (8) can move a tip portion (8c) forward and backward relative to a needle bed gap (2) through pivotal displacement by setting, as a support point, a concave portion (5a) of a needle plate (5). A wire spring (10) energizes the movable sinker (8) so that the tip portion (8c) is moved forward into the needle bed gap (2). A stopper (20) on which an abutment portion (8e) of the tip portion (8c) of the movable sinker (8) abuts to control the movable sinker (8) to be pivotally displaced by the energization of the wire spring (10) is provided in a position in the bottom portion of the base (4) near the needle bed gap (2). The maximum amount of press-in of the tip portion (8c) of the movable sinker (8) is regulated by an abutment of the abutment portion (8e) on the stopper (20). The stopper (20) can adjust a forward and backward movement amount relative to the needle bed gap (2) by a position adjusting mechanism (21).