To prohibit improper switching of a looper-threading/stitch-forming switching mechanism to a stitch-forming state during the gas supply operation of a gas supply pump when loopers are threaded by a one-touch operation.

A gas-conveyed threading device for a sewing machine includes: a clutch 60 for transmitting power from a sewing machine motor M to a drive shaft 5 for driving a stitch-forming device 30 including loopers 7, 8 and 9 when stitches are formed or to a gas supply pump 41 when the loopers are threaded; a looper-threading/stitch-forming switching mechanism 90 for switching the clutch so as to block power transmission to the stitch-forming device and transmit power to the gas supply pump when the loopers are threaded, and so as to transmit power to the stitch-forming device and block power transmission to the gas supply pump when stitches are formed; and a switch-prohibiting mechanism 160 for prohibiting improper switching of the looper-threading/stitch-forming switching mechanism to the stitch-forming state during the gas supply operation of the gas supply pump.