An exhaust pressure measuring device including a connection pipe connected to a middle of an exhaust line for carrying byproduct gas, the connection pipe having an opening formed in a middle of a body thereof; a chamber provided at an outer side of the connection pipe and communicating with an inside of the connection pipe through the opening, the chamber having a nitrogen supply line connected thereto, the nitrogen supply line allowing nitrogen gas to be supplied from the outside; and a pressure sensor installed to the chamber to measure pressure in the chamber, whereby a change of exhaust pressure in the exhaust line is measured from the measured pressure in the chamber.