Need experts' advice

Hello friends..
I am not a big gaming fan, but playing Final Fantasy XII for a last few days and I must admit that it's really an great game. Well, I got it from Dealrocker.com with a new PlayStation 3. Can anyone explain me why I am losing some of my maximum life points after equipping better armors and helmets? I really don't have any idea why it's happening?

Thanks in advance for your inputs.

Maybe the equipment you had before gave more HP. Check the HP number and the small number above when equipping something, it tells you what your HP will be when you equip it.