To expand a region in which an appropriate operation is enabled to both a low load side and a high load side.

This premixed compression self-ignition type internal combustion engine 1 comprises a first intake port In1 and a second intake port In2. The first intake port In1 serves as a straight port and is constituted such that an intake air flowing in a cylinder 3 via that first intake port In1 flows along a cylinder wall to generate a swirl Sw1. The second intake port In2 is constituted such that the intake air is made to flow in the vicinity of a center part of the cylinder, and is arranged in a helical port so as to generate a swirl Sw2 which is in the same direction as the swirl Sw1. A fuel injection port 10 is arranged so as to supply a fuel to the second intake port In2. As a result, in a pre-mixed gas inside the cylinder 3, a fuel concentration nonuniformity is formed such that the pre-mixed gas is thick near the center part and is thin at an outside of the cylinder 3.