By William Horobin

PARIS--Confidence in France's manufacturing sector rose in May to the highest level in nearly four years as business leaders revised up their assessment of recent output.

Confidence in the manufacturing sector rose further above the long-term average of 100 to reach 103 in May, the highest level since August 2011, statistics agency Insee said. The figure for April was revised to 102 from 101 previously.

A wider measure of business confidence--including wholesale, construction, retail and services--also rose. The combined indicator rose to 97 from 96 in April, Insee said.

Write to William Horobin at william.horobin@wsj.com