To enable the operation under a low load to be stabilized, and the operating performance at the time of high load to be ensured by a simple configuration.

A partition wall 19 is arranged in the downstream of an intake air passage 9 connected to a combustion chamber 8 of an engine to divide the intake air passage 9 into a low load passage 9b and a high load passage 9c, and a throttle valve 21 which fully opens and closes the intake air passage 9 to switch between the low load passage 9b and the high load passage 9c, is provided. Then, a fuel injection device 26 which is set to allow the intake air to flow into the low load passage 9b partitioned by the partition wall 19 when the degree of opening of the throttle valve 21 is low, and which injects fuel to the intake air flowing in the low load passage 9b, is arranged-installed.