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 inserting a looper thread (16a, 16b, 16c) which is led to the looper (7, 8, 9), a hollow looper thread guide (130, 7e, 8e, 9e, 7f, 8f, 9f) extending from the looper thread introduction mechanism to the looper thread inlet (7a, 8a, 9a) and having a looper thread guide outlet (7d, 8d, 9d), a gas supply pump that a looper threading of the looper thread is performed from the looper thread introduction mechanism to the looper thread guide outlet through the hollow looper thread guide by gas carrying, characterized by: a clutch for respectively transmitting power from a sewing machine motor to a drive shaft driving a stitch forming device including the looper at a time of stitch forming or to the gas supply pump at a time of looper threading, and a looper threading/stitch forming changeover mechanism for changing over the clutch so that transmission of the power to the stitch forming device is interrupted and the power is transmitted to the gas supply pump at a time of looper threading and so that the power is transmitted to the stitch forming device and the transmission of the power to the gas supply pump is interrupted at a time of stitch forming. 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 inserting a looper thread (16a, 16b, 16c) which is led to the looper (7, 8, 9), a hollow looper thread guide (130, 7e, 8e, 9e, 7f, 8f, 9f) extending from the looper thread introduction mechanism to the looper thread inlet (7a, 8a, 9a) and having a looper thread guide outlet (7d, 8d, 9d), a gas supply pump that a looper threading of the looper thread is performed from the looper thread introduction mechanism to the looper thread guide outlet through the hollow looper thread guide by gas carrying, characterized by: a clutch for respectively transmitting power from a sewing machine motor to a drive shaft driving a stitch forming device including the looper at a time of stitch forming or to the gas supply pump at a time of looper threading, and a looper threading/stitch forming changeover mechanism for changing over the clutch so that transmission of the power to the stitch forming device is interrupted and the power is transmitted to the gas supply pump at a time of looper threading and so that the power is transmitted to the stitch forming device and the transmission of the power to the gas supply pump is interrupted at a time of stitch forming. a clutch for respectively transmitting power from a sewing machine motor to a drive shaft driving a stitch forming device including the looper at a time of stitch forming or to the gas supply pump at a time of looper threading, and a looper threading/stitch forming changeover mechanism for changing over the clutch so that transmission of the power to the stitch forming device is interrupted and the power is transmitted to the gas supply pump at a time of looper threading and so that the power is transmitted to the stitch forming device and the transmission of the power to the gas supply pump is interrupted at a time of stitch forming.