German investors are less optimistic on the outlook of German economy, a survey revealed on Tuesday.

The Mannheim-based Centre for European Economic Research (ZEW) released its latest index measuring investors confidence for economy in the coming six months, showing that the index fell by 2.2 points compared to the previous month and stood at 36.3 points-mark.

The drop was unexpected, as economists had forecast the index would rise to 40 points. The current value, however, was higher than historical average of 23.7 points.

"The financial market experts stick to their overall positive forecast," said ZEW president Prof Clemens Fuest. "This illustrates their confidence in the robustness of the German economy despite the rather weak figures concerning industrial production and foreign trade released recently," he added.

Industrial output in Europe's largest economy fell by 1 percent in May. Exports to other countries dropped by 2.4 percent.

Following a drop of 0.7 percent in the last quarter of 2012, the German economy was expected to recover in 2013. Private consumption was considered as the main growth engine. In the first three months this year, however, German economy only grew by 0.1 percent, as most parts of the country was still in an extremely long and cold winter.

Bundesbank, the central bank of Germany, predicted the German economy would improve further in the second quarter. German government forecast gross domestic product would grow by 0.5 percent in 2013 and 1.6 percent in 2014.