An apparatus to change liquid light aromatic hydrocarbon into gaseity includes a gas storage barrel, two gas generation barrels and two gas connection pipes connected between the gas storage barrel and the respective gas generation barrels to form a “π” shape. Each gas generation barrel includes a light aromatic hydrocarbon filling pipe, an air supply pipe, an air intake pipe, an aeration pipe, and a heating member. A liquid communicating pipe is connected between the two gas generation barrels. The apparatus of the present invention is to mix and gasify liquid fuel, such as ether or alkanes, and air as combustion gas. During heating, the fuel can be resupplied to stable the quality of the output gas.