Hi Tania-chan,
It says, starting from the righthand side, "isamashii bosu no tenka" which means "the brave boss's world". Note, it literally says the English word "boss" (bosu). Also, 'world' is a fairly crude translation of 'tenka', which literally means 'under heaven'. Another way to translate 'tenka' is 'descent from heaven', so it could also mean "the brave boss's decent from heaven".
Also, it seems to be written backwards, which is why I was having trouble reading it at first. Anyone out there know the significance of that?