To suitably reduce fuel consumption ratio in all operation zone and achieve requested power performance of a vehicle.

This engine is provided with a first intake air passage 7 in which air from an outside flows, a compressor 8 compressing air from the outside, a cooling device 9 cooling the compressed air, an expander 10 expanding the cooled air, an intake air introducing pass (a second intake air passage 11, an intake manifold 2) introducing expanded air to combustion chambers 1A-1D, a bypass passage 13 keeping communication between the first intake air passage 7 and the second intake air passage 11, a flow passage change over valve 14 leading air form the outside to either of the compressor 8 or the bypass passage 13, and a control means 15 changing over the flow passage change over valve 14 to lead air from the outside to the compressor 8 at a time of operation in a low and middle speed zone and changing over the flow passage change over valve 14 to lead air from the outside to the bypass passage 13 at a time of high output request.