In a gas-mixture-nonuniformity acquisition apparatus for an internal combustion engine, the nonuniformity of fuel concentration within a gas mixture is acquired under the assumption that, in a process in which a cylinder interior gas taken into a combustion chamber of the engine and fuel injected into the combustion chamber mix together to form a gas mixture, a collision reaction repeatedly takes place within the gas mixture in such a manner that, due to collision of two gas volumes having different fuel mass ratios, respective portions of the two gas volumes mix together, and the mixed portions separate from the corresponding gas volumes and form a portion or the entirety of another gas volume having a fuel mass ratio different from those of the two gas volumes.