Provided is a weft knitting machine equipped with a movable sinker wherein a sufficient depression force can be obtained through a simple arrangement even under a closed state. A movable sinker (50) includes a sinker (51), a sinker jack (52) and a wire spring (53). The wire spring (53) abuts on the tip (52a) of the sinker jack (52) and is supported thereby. The wire spring (53) presses the tip (52a) of the sinker jack (52) from the surface side on the tooth mouth (2) side and presses the tip (52a) to clamp from the back side through a passive arm (51e) of the sinker (51), both under open state and closed state of the sinker (51) so long as a load is not applied to a knitting yarn receiver (51d). Consequently, the fabric of the tooth mouth (2) can be depressed with a depression force of the substantially same level as that under open state even if the stroke of the sinker (51) increases under closed state.