The present invention is a translation support system for supporting machine translation from a source-language sentence into a target-language sentence, the translation support system including an input unit that accepts an input of a source-language sentence to be translated; an error database that at least stores words or combinations of words included in a plurality of source-language sentences for which machine translation from the source-language sentences into target-language sentences is not performed correctly; a controlled-source-language-sentence database that stores a plurality of source-language sentences as well as controlled source-language sentences, which are source-language sentences that are controlled, corresponding to the plurality of source-language sentences and expressed in a format satisfying predetermined conditions; a control unit that classifies whether or not the input source-language sentence is machine-translatable; and an output unit that is capable of outputting the input source-language sentence classified as being non-machine-translatable.