To provide a weft inserting device in an air jet loom, capable of enhancing weft driving force in a weft inserting nozzle, without substantially changing an existing layout.

This weft inserting device in the air jet loom is equipped with the weft inserting nozzle 10 which draws the weft Y out of a weft length-measuring and weft-storing device 5 connected to a yarn supply part, by jetting a compressed air flow, and inserts the weft W into a shed of the warp, wherein the weft inserting nozzle 10 is structured by arranging a first weft inserting nozzle 11 and a second weft inserting nozzle 12 in series and a weft yarn guide of an accelerating tube 14 of the second weft inserting nozzle 12 is formed out of a yarn guide in a direction of firstly inserting the weft from a straight-line part 14a to a circular yarn guide D1, a yarn guide in a direction of oppositely inserting the weft for transporting the weft to an opposite weft-inserting side in a circular yarn guide D2, and a yarn guide in a direction of secondly inserting the weft from a circular yarn guide D3 to a straight-line part 14b arranged in this order.