A message processing device (10) includes an estimator (11), an extractor (12), and an indicator (13). The estimator (11) estimates words understandable to a destination user (1). The extractor (12) extracts, from a message (3) created by a transmission originator user (2), a portion that does not match the words estimated by the estimator (11). The indicator (13) indicates, to the transmission originator user (2), the message (3) with the extracted portion by the extractor (12) being in an emphasized manner.
