A door machine of a fireproof door comprises an input end to be actuated by an input axle; an output end loaded with weight of door panels, the loading force of which is transmitted back to a central axle through an output axle; a clutch mechanism normally connecting the central axle with the input axle together; a brake mechanism including a torsion spring which is integrated with the input axle of the input end and one end of which bears the loading force came from the central axle to shrink the inner diameter thereof so that the input axle is in an immobilized state; when an external force is applied to the input end, the other end of the torsion spring resisting against the weight of the door panels to expand the inner diameter thereof so that the input axle is rotated.