A gas carrying threading device of sewing machine comprising: at least one looper (7,8,9) having a hollow structure from a looper thread inlet (7a,8a,9a) to a looper loop-taker point thread outlet (7b,8b,9b), a looper thread introduction mechanism for inserting a looper thread (16a,16b,16c), a hollow looper thread guide (130, 7e, 8e, 9e, 7f,8f,9f, 7g,8g,9g) extending from said looper thread introduction mechanism to said looper thread inlet and having a looper thread guide outlet (7d,8d,9d), a gas supply pump for looper threading of said looper thread from said looper thread introduction mechanism to said looper thread guide outlet through said hollow looper thread guide by the gas carrying, a clutch for transmitting power from a sewing machine motor to a drive shaft for driving a stitch forming device including said looper at the time of the stitch formation and to said gas supply pump at the time of the looper threading respectively, and a looper threading/stitch forming changeover mechanism for changing over said clutch to transmit the power to said gas supply pump at the time of the looper threading and to transmit the power to said stitch forming device at the time of the stitch formation depending on a manual operation of a looper threading/stitch forming changeover manual operating portion, characterized in that said clutch comprises: a gas supply drive member for transmitting the power to said gas supply pump, having an engaging and biting claw, a stitch forming drive member fastened to said drive shaft for transmitting the power to said stitch forming device, having an engaging claw, a clutch hollow shaft fitted on said drive shaft and driven rotatably by said sewing machine motor, and a changeover slide sleeve fitted around an outer circumference of said clutch hollow shaft, connected slidably thereto, and rendered to slide to one of the gas supply drive member and the stitch forming drive member slides depending on the manual operation of said looper threading/stitch forming changeover manual operating portion, having an engaging and biting claw to engage and bite mutually with said engaging and biting claw and thereby to retain the connecting state for connecting to said gas supply drive member and having an engaging claw to engage mutually with said engaging claw for connecting to said stitch forming drive member. at least one looper (7,8,9) having a hollow structure from a looper thread inlet (7a,8a,9a) to a looper loop-taker point thread outlet (7b,8b,9b), a looper thread introduction mechanism for inserting a looper thread (16a,16b,16c), a hollow looper thread guide (130, 7e, 8e, 9e, 7f,8f,9f, 7g,8g,9g) extending from said looper thread introduction mechanism to said looper thread inlet and having a looper thread guide outlet (7d,8d,9d), a gas supply pump for looper threading of said looper thread from said looper thread introduction mechanism to said looper thread guide outlet through said hollow looper thread guide by the gas carrying, a clutch for transmitting power from a sewing machine motor to a drive shaft for driving a stitch forming device including said looper at the time of the stitch formation and to said gas supply pump at the time of the looper threading respectively, and a looper threading/stitch forming changeover mechanism for changing over said clutch to transmit the power to said gas supply pump at the time of the looper threading and to transmit the power to said stitch forming device at the time of the stitch formation depending on a manual operation of a looper threading/stitch forming changeover manual operating portion, a gas supply drive member for transmitting the power to said gas supply pump, having an engaging and biting claw, a stitch forming drive member fastened to said drive shaft for transmitting the power to said stitch forming device, having an engaging claw, a clutch hollow shaft fitted on said drive shaft and driven rotatably by said sewing machine motor, and a changeover slide sleeve fitted around an outer circumference of said clutch hollow shaft, connected slidably thereto, and rendered to slide to one of the gas supply drive member and the stitch forming drive member slides depending on the manual operation of said looper threading/stitch forming changeover manual operating portion, having an engaging and biting claw to engage and bite mutually with said engaging and biting claw and thereby to retain the connecting state for connecting to said gas supply drive member and having an engaging claw to engage mutually with said engaging claw for connecting to said stitch forming drive member.