The guidelines and application forms are available on the website of the Graduate School of Science of Osaka University:

If you want to apply, keep in mind that the first thing applicants must do is selecting the research group(s) they want to work in and contact the professor(s) of the group(s) in order to obtain a "Letter of Conditional Acceptance". The first contact should happen as soon as possible and at the latest four weeks before the application deadline. The list of groups is found here.

Please contact us if you have any question or need help in contacting the professors.
Additional material
Examination questions assigned in previous years can be found below:

Entrance examination 2010
Entrance examination 2011
Entrance examination 2013
Entrance examination 2014

Department of Physics, Graduate School of Science
Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Osaka, Japan