I live in
Italy and don't think using a metal detector is illegal (I am not a lawyer, but I am pretty sure you can UNLESS you do it on an archeological site, I mean: if you have some fields you can use it there, but if you go to a site you'll be in trouble).
However, let's say you own a
field, you metal-detect it. OK. You spot something, you start digging... well... uhm... I'd cover the MD in a bag before stating to dig, because even if the
field is yours you cannot dig for antique items unless you are authorized, an archeologist working for a research project with the local museum etc.
So let's say the MD is sealed now in a bag and you are digging in your
field. You might just be wanting to
plant a tree, no one will ever ask you anything, not even the most paranoid of your neighbors. OK
Let's say you find some
roman coins, pretty likely in many parts. But even if you found them in your
field, they are NOT yours, they belong to the
Italian State (which indeed would throw them soewhere in a storehouse, unless you find something realy exceptional). Anyway you would not be allowed to take them
home, it would be an illegal export of archeological "treasures" belonging to the state. Well, if you find a
roman bronze I don't think a policeman will materialize on the spot and take it away, but the law says you cannot put that coin in your bag.
Although I really doubt anyone would ever open your bag in the airport and strip you naked to check for coins, and be able to separate
fakes from original if you throw them all in the same box, and even care if those coins are not precious... They will check for terrostist, not for hobby-diggers. But just be warned that it is not legal, so it's up to you.