The present invention relates to a coupling structure of a case and an air heater body in an air heater, and the coupling structure includes: an air heater body for generating flames with the fuel supplied from a fuel tank and forcedly blowing the heat of the flames to the outside; the case detachably coupled surroundingly to the air heater body; fastening screws for unitarily coupling the air heater body and the case to each other; coupling flanges formed on both sides of the case in a longitudinal direction of the case and having first screw coupling holes screw-coupled to the fastening screws; and coupling brackets located on one side and the other side of the air heater body in the longitudinal direction of the air heater body in such a manner as to come into surface contact with the coupling flanges and having second screw coupling holes formed thereon correspondingly to the first screw coupling holes.