Germany's growth forecast for 2015 has also been downgraded
Shoppers in Europe's largest economy are feeling nervous about the coming months.
The monthly index compiled by GfK market research dropped from 9.5 at the end of February to 9.4 heading into April.
Analysts polled by Reuters had expected the reading to remain at 9.5.
"The weak demand for German products in certain important markets will probably not leave economic growth in Germany unaffected," said GfK analyst Ralf Buerkl.
He pointed to particular concerns about slowing economic activity in China and the United States as factors clouding the economic outlook in Germany.
Yesterday the German government's panel of economic advisors revised their growth forecast, down by 0.1% for 2015, to 1.5%.
Last year the country economy grew by 1.7% as private consumption and public spending increased.
The GfK still expects personal consumption to increase by 2% in real terms during 2015.