You can check unknown words by dictionary. But how do you check grammar? 「基礎日本語文法教本 (Understanding Basic Japanese Grammar) 」is an ideal grammar reference book for basic and intermediate learners (JLPT N3, N4 and N5) . With this book, you can check and understand grammar easily as, besides the clear explanation, there's plenty of practical example sentences.
In this book, One and Two are the introductory stages, Three and Four are the Expanding stages and Five and Six are the Advanced Stages. The Table of Contents is 12-page long and is very thorough. It shows exactly what grammar will be discussed on each page of the book with the structure written in Japanese and the meaning summarized in English. For example, 「いつ」on page 28. This is very useful as a reference book for grammar.
Other good points of this book:
Simple explanation of grammar points
A lot of example sentences, paragraphs and conversations
Great English translations into English (There is a Chinese edition too, if you prefer)
It follows the grammar and vocabulary guidelines for JLPT N3, N4 and N5
Furigana for kanji
It containts a CD
Please note that this book is not for self-study. Explanation of each grammar is too simple to learn new expressions without guidance of teacher.
Students who need this book are those who: