Substrate processing device, cooling unit, and heat insulating structure

A configuration provided with: an intake pipe which is provided for each zone to supply a gas for cooling a reaction pipe; a control valve with which the intake pipe is provided to adjust the flow volume of the gas; a buffer portion in which the gas supplied from the intake pipe is temporarily accumulated; and opening portions which are provided in the zone at regular intervals in a circumferential direction so as to blow out the gas accumulated in the buffer portion toward the reaction pipe. In the configuration, the flow volume of the gas introduced into the intake pipe is set in accordance with a length proportion in the vertical direction of the zone, thereby adjusting the flow volume and flow velocity of the gas, which is ejected out of the opening portions toward the reaction pipe by opening or closing the control valve.