He was apparently angry at members of his staff.
Initial investigation revealed that Paisan Saengnarai, 58, chief of tambon Na Ngua, had consumed alcohol at a restaurant before arriving at the scene.
Upon arrival at the pub, he reportedly had a conflict with members of his staff, so returned to his car to get his gun and began shooting until he was overpowered by others.
The pub is located along Highway No 212 in Ban Phaeng district and the case is being processed by Ban Phaeng police.