A sinker device of a weft knitting machine, wherein a movable sinker (8) can move a tip part (8c) forward and backward relative to the mouth part thereof (2) by the swing displacement of a needle plate (5) about the recessed part (5a) thereof. A wire spring (10) energizes the movable sinker (8) so that the tip part (8c) can move forward to the mouth part (2). A stopper (20) allowing the contact portion (8e) of the tip part (8c) of the movable sinker (8) to abut thereon to restrict the swing displacement of the movable sinker (8) by the energization of the wire spring (10) is installed at the bottom part of a base (4) near the mouth part (2). The maximum pressed amount of the tip part (8c) of the movable sinker (8) is limited by the contact of the contact portion (8e) with the stopper (20). The stopper (20) is so formed that the forward and backward movement amounts thereof relative to the mouth part (2) can be adjusted by a position adjusting mechanism (21).