Carwyn Jones says Wales benefits from being part of UK
The first minister says people should not pretend that independence for Wales would be a good thing.
Carwyn Jones told the BBC Wales that being part of the UK "gives us a much stronger voice on the world stage".
He urged Prime Minister David Cameron not to interfere in the timing of any Scottish referendum on independence.
Mr Jones argued Wales and Northern Ireland would need more MPs and peers at Westminster in the event of a Scottish breakaway.
Debate on the future of the United Kingdom has been fuelled by the Scottish National Party's declared intention to hold a referendum on independence in 2014.
Speaking on the Sunday Politics programme, Mr Jones said that if Scotland became independent, the relationship between Wales and the rest of the UK would have to change but this wouldn't mean independence.
"Let's not pretend that it would be a good thing for Wales to become independent," he said.
"We know financially that it's not in our interests. We know that being part of the UK gives us a much stronger voice on the world stage. And money is transferred from richer parts of the UK into Wales."
The first minister said the opinion polls indicated that the people of Scotland would not back independence at the moment but warned the prime minister not to interfere.
"The opinion polls say that if a referendum was held in Scotland now, there would be a no vote.
"But what does worry me though is that the UK government has to be extraordinarily careful in not giving the impression that it's trying to interfere in the timing and the question for a Scottish referendum.
"That's a matter for the people of Scotland."
He also rejected criticism from the Welsh Secretary Cheryl Gillan, who accused him of pursuing an "isolationist agenda".
"The view seems to be expressed that if we do anything different here in Wales, then we're on the road to independence," he said.
"That's a very dangerous argument because what it's saying is that devolution can never work even though the people of Wales have voted twice for devolution.
"As somebody who was elected by the people of Wales, I think I have a mandate to take forward a programme of government in a way that the Secretary of State - who wasn't elected by the people of Wales - doesn't.
"Now I want to work with the UK government where I can, but saying 'you can do what you want in Wales but if you do, you must be some kind of separatist' is not a wise argument.
Mr Jones added that if Scotland did back independence, then an increase in the number of MPs from Wales and Northern Ireland would have to considered along with increased representation in the Lords.
On Friday, the first minister proposed a new upper house similar to the US Senate with equal representation for England, Wales and Northern Ireland to limit English domination in the event of Scottish independence.
For the Conservatives, AM Nick Ramsay told the Sunday Politics that the issue of Scottish independence was a matter for the Scottish government and ultimately the people.
But he said the prime minister was right to take a position on such a important matter for the whole of the UK.
"There is also a duty on the UK government to make sure that before any referendum is held that there isn't any instability," he said.
"David Cameron has said that this referendum should be held sooner rather than later and I agree with that."