Although I'm not decided to take it, I decided to know around GMAT with the book below.
http://www.amazon.co.jp/gp/aw/d/4757422172/ref=mp_s_a_1_1?qid=1378392156&sr=8-1&pi=AC_SX110_SY165
It's a bit high, but spending some money will encourage me to put effort into knowing it.