A weft insertion method using a weft insertion device in a water jet loom that includes a measuring and storing device including a storage device having a rotary yarn guide continuously driven to rotate and a storage drum on which a weft is wound and stored by a rotation of the rotary yarn guide, and a measuring device having a measuring roller which continuously feeds the weft from a yarn feeder toward the rotary yarn guide at a predetermined feed speed corresponding to a weft insertion length, a weft insertion related device which is involved in a weft insertion and affects a timing at which the weft starts to fly or a state where the weft flies, and is driven according to a set value stored in a set value storage, and a weft insertion device including the set value storage and a weft insertion control device for controlling drive of the weft insertion related device, in which one weft insertion is performed through a constrained flight process in which the weft flies while being constrained by a feed speed of the measuring roller by being in a state where the weft is drawn directly from the rotary yarn guide without passing through the storage drum, after a free flight process in which the weft flies in a free flight state by being drawn while the weft on the storage drum is released from the storage drum, in which the weft insertion device includes a weft detection sensor provided so as to face the storage drum and detecting a passage of the weft to determine a passage timing which is a passage timing of the weft circulating around the storage drum with the weft insertion, the weft insertion method comprising: setting in advance a reference value of a set position arrival timing in association with a set arrival position, regarding the set arrival position, which is an arrival position at which a leading edge of the weft reaches in a weft insertion process including an end time of the weft insertion, and is one of a plurality of arrival positions where a timing at which the leading edge of the weft reaches the arrival position can be determined from the passage timing in the free flight process, and the set position arrival timing at which the leading edge of the weft reaches the set arrival position; and determining the passage timing based on a detection signal output from the weft detection sensor in the weft insertion during weaving, determining an actual value of the set position arrival timing from the passage timing, comparing the determined actual value with the reference value, and in a case where a deviation occurs between the determined actual value and the reference value, determining a correction amount of the set value based on the deviation so as to change a driving mode of the weft insertion related device so that the deviation decreases. the weft insertion device includes a weft detection sensor provided so as to face the storage drum and detecting a passage of the weft to determine a passage timing which is a passage timing of the weft circulating around the storage drum with the weft insertion, the weft insertion method comprising: setting in advance a reference value of a set position arrival timing in association with a set arrival position, regarding the set arrival position, which is an arrival position at which a leading edge of the weft reaches in a weft insertion process including an end time of the weft insertion, and is one of a plurality of arrival positions where a timing at which the leading edge of the weft reaches the arrival position can be determined from the passage timing in the free flight process, and the set position arrival timing at which the leading edge of the weft reaches the set arrival position; and determining the passage timing based on a detection signal output from the weft detection sensor in the weft insertion during weaving, determining an actual value of the set position arrival timing from the passage timing, comparing the determined actual value with the reference value, and in a case where a deviation occurs between the determined actual value and the reference value, determining a correction amount of the set value based on the deviation so as to change a driving mode of the weft insertion related device so that the deviation decreases. setting in advance a reference value of a set position arrival timing in association with a set arrival position, regarding the set arrival position, which is an arrival position at which a leading edge of the weft reaches in a weft insertion process including an end time of the weft insertion, and is one of a plurality of arrival positions where a timing at which the leading edge of the weft reaches the arrival position can be determined from the passage timing in the free flight process, and the set position arrival timing at which the leading edge of the weft reaches the set arrival position; and determining the passage timing based on a detection signal output from the weft detection sensor in the weft insertion during weaving, determining an actual value of the set position arrival timing from the passage timing, comparing the determined actual value with the reference value, and in a case where a deviation occurs between the determined actual value and the reference value, determining a correction amount of the set value based on the deviation so as to change a driving mode of the weft insertion related device so that the deviation decreases.