Provided is a method of increasing an amount of coke-oven gas, including the step of: introducing steam into a gas way of a carbonization chamber of a coke oven such that a water-gas reaction is conducted at 500° C. or higher during a process of carbonizing coal in the carbonization chamber of the coke oven, wherein the starting point of steam into the gas way is moved up prior to a time point at which an amount of generation of coke-oven gas is maximized, so as to increase the steam introduction time, thereby maximizing a reaction of steam with carbon existing in the carbonization chamber of the coke oven.