本論文以LARP作文語料庫為對象，探究台灣JFL學習者「焦點詞」的習得狀況。研究結果發現：1）習得順位為「も1／は／だけ」→「も2／ばかり」→「しか」→「など1」→「さえ1」→「まで」→「くらい／こそ」。2）被聚焦的文法詞類中，有3分之2在第1期就已陸續出現;而「述語VP＋F(焦點詞)」的進展順序，則是「V-(r)u＋F」→「V-te＋F＋いる」與「V-(i)＋F＋する」。3）在偏誤用法方面，與被聚焦的文法詞類相關的，有「聚焦主格型」、「NP・PP混淆型」、「NP・PP以外文法詞類混淆型」等3種偏誤發生;而與焦點詞相關的，則有「も1的過度使用」以及「結構的錯誤」等2種現象發生。焦點詞的習得順位、使用次數、習得難易三者間有密切關聯;而學習者是否使用與焦點詞相關的句構，除了和學習準備度有關外，也和學習者的類型（亦即學習者是否為「謹慎型」）有關。此外，「聚焦主格型」的偏誤則是一種母語遷移現象。

The present paper, based on LARP composition corpus, aims at clarifying the route and rate of the acquisition of the focus particle by Taiwanese JFL learners. The research has led to the following findings: 1) The acquisition order goes as ＂mo1・wa・dake＂→＂mo2・bakari＂→ ＂shika＂→＂nado1＂→＂sae1＂→＂made＂→＂kurai・koso.＂ 2) Two thirds of the focused elements emerge in phase 1, and concerning the development of the form of ＂predicate VP+F(focus particle),＂ it goes as ＂V-(r) u+F＂→ ＂V-te+F+iru＂ as well as ＂V-(i)+F+suru.＂ 3) Three types of misuses of focused elements, namely ＂focus-on-subject type,＂ ＂NP-PP confusion type,＂ and ＂confusion of the other parts beyond NP-PP type,＂ as well as two types of misuses of focus particle, namely ＂overuse of mo1＂ and ＂structural mistake,＂ are found. It shows a correlation between the order of acquisition, the frequency of use, and the degree of difficulty of the particles. The development of focus particle has to do with not only readiness but also the type of the learner, namely whether the learner is of a prudent type or not. Moreover, ＂focus-on-subject type＂ of misuse is considered a form of mother tongue transfer.