As part of a whistlestop tour of the East Midlands, he called at Progressive Rail at Sandiacre where he briefly spoke with employees before being quizzed by the press.
Mr Cameron, who is spearheading the campaign for Britain to remain as part of the European Union said the East Midlands would only benefit by staying put.
When asked by the Chad how Nottinghamshire and Derbyshire would benefit in terms of employment, he said: “We benefit because we have access to a home market of 500 million people and that’s good for jobs in manufacturing, jobs in services and good for jobs (as a whole).
“Here (Progress Rail) we are at a good manufacturing business, a business that is the product of US investment into the UK and is benefiting from open markets in Europe.
“As I was walking round I met someone from the French industry looking to come to buy from here, and that’s a classic example of how we want foreign-owned company to invest in Britain and they do that because we are part of the single market.
“We want that single market open for business and jobs - were we to leave it would be bad for manufacturing jobs.”
Progress Rail, which was founded in the USA in 1982 and is a subsidiary of construction company Caterpillar.
The precision engineering company supplies rail track and transit system products.
However, Mr Cameron says manufacturing support is only one reason for the East Midlands to remain within the EU.
With the referendum planned for June 23, he said that opting out of Europe would close off opportunities across the board.
“I would argue for young people voting for the first time and looking to grow up in the United Kingdom, the EU is about opportunity,” he said.
“It gives you the opportunity to work, trade and travel anywhere across the 28 countries - your opportunities are greater and I think that’s a key argument.
“I think the most important argument, frankly, is the economy.
“There’s a range of experts now saying we’re better off in and worse off out, is truly impressive.
“Either this is some giant international conspiracy or all of these organisations are making a good, strong argument that we’re better off having access to a market of 500 million people.
“The economy would be poorer if we had less access to our principal market and that to me is the key at the heart of