1. A machine-translation apparatus using multi-level verbal-phrase patterns, comprising: a basic verbal-phrase pattern database storing therein basic verbal-phrase patterns; a default verbal-phrase pattern database storing therein default verbal-phrase patterns; a default word-order verbal-phrase pattern database storing therein default word-order verbal-phrase patterns; a default preposition database storing therein default preposition patterns; a simple sentence generation unit for generating, by recomposing an input sentence, an input simple sentence having a structure of verbal-phrase patterns; a basic verbal-phrase pattern-matching unit for trying a match of a semantic code of each case component of the input simple sentence with the basic verbal-phrase patterns; a default verbal-phrase pattern matching unit for trying, if the basic verbal-phrase pattern-matching unit fails a complete match, a match of a size and case prepositions of the input simple sentence with the default verbal-phrase patterns having a verb identical to that of the input simple sentence; a default word-order matching unit for trying, if the default verbal-phrase pattern matching unit fails a complete match, a match of a word-order of the input simple sentence with the default word-order verbal-phrase patterns having a case component structure identical to that of the input simple sentence; and a default preposition matching unit for generating, if the default word-order verbal-phrase pattern matching unit succeeds in a complete match, a target sentence of the input sentence with the default preposition patterns having a context identical to that of the input simple sentence.