Complete and save the game on any difficulty setting. Start a new game from the saved game file, and wait until the starting sequence ends. After Rain leaves, you should see a small control pad on the left-hand wall immediately after the screen switches. Walk up to it and the Use option should appear. Press the Triangle. Enter one of the following codes to activate the cheat function.

Enter these at the small control pad:

All weapons - 11692
Infinite ammunition - 61166
Big head mode - 10397