A brake release device attached to a door machine comprises a ring plate provided with a plurality of openings and fixed on a pull chain disc, a base plate located at the outside of the door machine, a passive plate provided with a plurality of plug pins that correspond to the openings of the ring plate and slides together with the sliding pin, a guiding member fixed together with the base plate, a sliding pin corresponding to a brake release bar for releasing brake of the door machine and slidably guided by the guiding member, a spring element and a fusible link device that curbs the sliding pin from leaving the brake release bar. By the spring element, the guiding member stores potential energy for sliding.