In a jet loom, a weft insertion start timing, a jet injection start timing of a main weft inserting nozzle and a jet injection stop timing of auxiliary weft inserting nozzles are controlled on the basis of empirical rules. A weft insertion control program incorporating the empirical rules is provided for a control computer for controlling an energization start timing of a solenoid, an energization start timing of an electromagnetic valve and a deenergization timing of an electromagnetic valve on the basis of the weft insertion start timing obtained from a weft release detector and the weft leading end arrival timing obtained from a weft detector. The control program is so prepared as to detect the control quantities for the detected data on the basis of specific correspondence relations between sequential arrayed data including a plurality of weft insertions start timing data and a plurality of weft leaving and arriving timing data, both data being classified in a particular order in accordance with empirical rules, and sequentially arrayed control quantities also classified in a particular order in accordance with an empirical rule.