The present invention relates generally to an additional function-expandable fire detector, and more specifically to an additional function-expandable fire detector that enables an additional function of providing a fire alarm in an early stage to be added through the combination of a semiconductor fire detector with a stand-alone module and also enables only an obsolete fire detector to be replaced in a one-to-one correspondence without the replacement of an overall existing fire detection system. The additional function-expandable fire detector includes: a body; a contactless output circuit unit that is installed in the body, that directly detects a fire, and that outputs an optical signal to the outside; and a stand-alone module that is coupled to the body, that detects the optical signal of the contactless output circuit unit, and that provides notification of the fire.