A translation-memory application method for automatic translation includes: generating TM-expanded forms by applying TM expansion rules respectively to source sentences whose morphemes have been analyzed; storing in an expanded TM database translated sentences corresponding to the generated TM-expanded source sentences; analyzing morphemes if an input sentence does not match any of the source sentences stored in basic TM database; generating a TM-expanded form by applying pertinent ones among the TM expansion rules to the input sentence whose morphemes have been analyzed; and producing, if the TM-expanded input sentence matches one of the TM-expanded source sentences stored in the expanded TM database, a translated output corresponding to the matched TM-expanded source sentence.