PURPOSE: To easily perform conversion of the unit of numerical expression in the case of machine translation.

CONSTITUTION: In addition to the conventional machine translation device, this device is provided with a unit conversion rule edit means 6 to edit a unit conversion rule, unit conversion rule storage means 7 to store the unit conversion rule, unit conversion executing means 8 to perform unit conversion, and character string designating means 9 to designate a character string to perform the unit conversion. When a source sentence is inputted and a translation executing means 3 is under execution, before editing or after editing, the unit conversion is calculated by the unit conversion executing means 8 and the translation is displayed on a display means 5.