Abstract: A gas filling device comprises a gas supplier configured to supply the gas to gas filler passages and a controller configured to separately open and close each of the valves provided in the respective gas filler passages, so as to control a gas flow supplied from the gas supplier, wherein the controller comprises a heat dissipation information acquirer configured to obtain heat dissipation information regarding heat dissipation capacity of each of the plurality of tanks and an in-tank information acquirer configured to obtain information regarding at least one of temperature and pressure in each of the plurality of tanks, and the controller is characterized to cause opening and closing the valves to allow communication between the separate gas filler passages, based on the heat dissipation information obtained by the heat dissipation information acquirer and the information in the tank obtained by the in-tank information acquirer.