Karl Gustaf Idman (1 December 1885 in Tampere – 13 April 1961 in Helsinki)[1] was a Finnish diplomat and a non-partisan Minister of Foreign Affairs in Antti Tulenheimo's cabinet in 1925.

Idman became an official in the Finnish Foreign Office in January 1918 after Finland gained independence.

Idman belonged to the delegation which visited St. Petersburg in 1917 and acquired Lenin's approval for Finnish Declaration of Independence.

During World War II, Idman hold a similar position of a special envoy since October 1939 in Tokyo and also since August 1941 in Mukden (Manchukuo).

He left in his will money for a foundation that distributes annually grants for approximate million euros to students in Tampere.