PURPOSE: To efficiently reduce the temperature of intake air supplied to an exhaust turbosupercharging engine, without supplying energy from the outside.

CONSTITUTION: A difuser 7 whose cross-sectional area gradually increases is interposed in a pipe passage 6 which reaches the intake manihold 4 of an engine 3 from the compressor 2 of an exhaust turbosupercharger 1 installed on an engine 3. Any increase in the number of parts can be suppressed by integrating the difuser 7 with the intake manihold 4. Consequently, since the intake air supplied via the pipe passage 6 from the compressor 2 of the exhaust thrbosupercharger 1 is adiapatically expanded during its passing through the difuser 7, temperature of the intake air supplied to the engine is effectively decreased without supplying energy from the outside.