After installing Mavericks on my MacBook Pro 2009 (japanese keyboard) the layout doesn't work. I mean if I press the @ button the è symbol comes out. I tried to change the layout in Preferences but doesn't work. Could anyone help me please?

Apple has changed the way Kotoeri keyboard layouts work. You should be able to get normal behavior if you activate the US layout and switch to that just before using Kotoeri. Here is also an Apple note on the topic with another suggestion:

http://support.apple.com/kb/TS5284

Be sure to tell Apple you want this changed back to the way if was in 10.8 and earlier via

http://www.apple.com/feedback

If you know Japanese well, you might ask on the Japanese discussions whether someone has found a better fix for this:

https://discussionsjapan.apple.com

10.9.1 has

Addresses an issue that may cause Japanese keyboards to retain a previously used language