1. A learning apparatus, comprising: one or more non-transitory storage media; and a computer, wherein: the one or more non-transitory storage media includes: a parallel corpus in which one or more pairs of original and translated sentences are stored, each of the one or more pairs having a source language sentence and a target language sentence that is a result obtained by translating the source language sentence; an element pair storage unit in which one or more element pairs are stored, each of the one or more element pairs being a pair of a source language element and a target language element; and a program, the program, when executed by the computer, causes the computer to function as: a parser unit that parses the target language sentence contained in the one or more pairs of original and translated sentences, thereby acquiring a binary tree of the target language sentence, the binary tree having one or more target language partial structures, each of which indicates the order of two or more elements forming the target language sentence and contains a parent node having a phrase label, and two child nodes, each of which is a child node of the parent node and has a target language phrase label or a target language element; a source language element acquiring unit that acquires, from the one or more element pairs in the element pair storage unit, one or more elements forming the source language sentence corresponding to the target language sentence, the one or more elements being one or more source language elements corresponding to target language elements that are child nodes at terminal ends of the one or more target language partial structures contained in the binary tree of the target language sentence; a source language partial structure acquiring unit that applies a structure indicated by the one or more target language partial structures contained in the binary tree of the target language sentence, to the one or more source language elements forming the source language sentence, thereby acquiring one or more source language partial structures, each of which indicates the order of two or more elements forming the source language sentence and contains a parent node having a phrase label, and two child nodes, each of which is a child node of the parent node and has a phrase label or a source language POS tag; a labeling unit that provides the one or more source language partial structures with a reordering label that is a label that enables to distinguish a source language partial structure, in which the order of two child nodes contained in a source language partial structure corresponding to a target language partial structure is different from the order of two child nodes contained in the target language partial structure from a source language partial structure, in which the order of two child nodes contained in a source language partial structure corresponding to a target language partial structure is the same as the order of two child nodes contained in the target language partial structure, thereby acquiring one or more labeled source language partial structures; a model building unit that builds one or more parsing models each having appearance probability information regarding a labeled source language partial structure, using the one or more labeled source language partial structures; an accumulating unit that causes the one or more non-transitory storage media to accumulate the one or more parsing models built by the model building unit; and a reordering unit that acquires, using the one or more source language partial structures each indicating the order of two or more elements forming the source language sentence, one or more source language partial structures, in each of which the two or more elements forming the source language sentence are reordered such that the order is close enough to satisfy a predetermined condition with respect to the order of the elements in the target language sentence, wherein the labeling unit provides the reordering label to the one or more source language partial structures reordered by the reordering unit.