FIRST try the casio website to check if manual is available for free download, enter
USERNAME:- casio
PASSWORD:- download

You can obtain your CASIO instruction manual by ringing casio on this number 0181 450 9131 Casio often will supply your manual free of charge but not always.

This information is updated frequently but please use the feedback form to tell me if it changes or to let me know any other useful information I could include on the site to help people obtain their manuals.

Alternatively

Casio: All models: Firstly, look on the back of your watch and
write down the four figure model code that you will see in a
little square. The G-Shock should be something like 1446 or 1449.
Go to
http://www.casio-europe.com/de/support/manuals/
Never mind that it's in German, ALL the manuals are in English.
Scroll down to "Uhren" (= Watches). Enter the four figure model
code into the box beneath it and click GO.
You will now have the manual - at last !!

Any casio manuals you can get directly from Instruction manuals UK are given below:-