Jo Swinson made the comment during questions in the House of Commons.
Labour has claimed for months that there is a crisis in living standards across the country.
But the charge has always previously been rejected by the Tory-Lib Dem Coalition.
Asked about Ms Swinson's comments, Downing Street refused to say that there was a cost of living crisis.
Mr Cameron's official spokesman said that the PM did accept that the UK was poorer because of the 2008-09 recession.
But on the equalities minister, he added: "I speak for the Prime Minister, she is a government minister".
Earlier in answer to a question from Labour's Sharon Hodgson, Ms Swinson had said: "The best way to tackle the cost of living crisis is to make sure that we get on with building a stronger economy that will support jobs and growth."
Last night Labour hailed Ms Swinson's comments.
Shadow Treasury minister Catherine McKinnell said: "Thank goodness one Minister has finally admitted there is a cost-of-living crisis under this government, but it's deeply worrying that David Cameron and George Osborne are so out of touch they are still in denial."
A Lib Dem spokesman said: "Squabbling over words won't make up for the fact Labour still don't have any credible economic policies. We have a serious and credible plan that is rebuilding the economy after the mess that Labour left behind."