In the case of a seat with an armrest on an automobile, an armrest lock mechanism may be released by, for example, the gravitational acceleration (G) in the event of vehicle collision. Accordingly, it is necessary to provide an anti-G spring for biasing to prevent the lock mechanism from being easily released. The purpose of the present invention is to provide an armrest unlocking device that enables a decrease in size of the anti-G spring. In order to solve the problem, provided is an armrest unlocking device in gear, the device operating such that the locking of the lock gear and the sector gear can be released by operating a lever link bracket so as to raise the lock gear, wherein the lock gear has a center of rotation thereof aligned with the position of the center of gravity.