An air-fuel ratio imbalance detection device for an internal combustion engine, characterized by comprising: output acquisition means for acquiring an output from an in-cylinder pressure sensor mounted on each of a plurality of cylinders of the internal combustion engine; calculation means for calculating a combustion parameter indicative of a combustion status within the plurality of cylinders based on an output of the in-cylinder pressure sensor, the output being acquired by the output acquisition means; injection amount control means for providing control to enlean an air-fuel ratio for each of the plurality of cylinders by reducing a fuel injection amount so that the combustion parameter calculated by the calculation means coincides with a predetermined value; and imbalance detection means for detecting an air-fuel ratio imbalance between the plurality of cylinders based on a reduction amount of fuel injection amount, the reduction amount being provided by control that is exercised for each of the plurality of cylinders by the injection amount control means, wherein the injection amount control means includes: means for calculating the reduction amount of fuel injection amount due to the control by the injection amount control means for each of the plurality of cylinder; means for acquiring a calculated value of an air-fuel ratio for the target cylinder based on the reduction amount of fuel injection amount, the calculated value of the air fuel ratio being an air fuel ratio of the target cylinder before the target cylinder is controlled by the injection amount control means; means for detecting an air-fuel ratio imbalance between the plurality of cylinders based on a comparison of the calculated values of the air-fuel ratios between the plurality of cylinders, and wherein the combustion parameter is at least one of quantities selected from a group of an in-cylinder pressure, internal energy, indicated torque, indicated work, a burning velocity, and the amount of generated heat, or a physical quantity correlated with at least one of the quantities selected from the group. output acquisition means for acquiring an output from an in-cylinder pressure sensor mounted on each of a plurality of cylinders of the internal combustion engine; calculation means for calculating a combustion parameter indicative of a combustion status within the plurality of cylinders based on an output of the in-cylinder pressure sensor, the output being acquired by the output acquisition means; injection amount control means for providing control to enlean an air-fuel ratio for each of the plurality of cylinders by reducing a fuel injection amount so that the combustion parameter calculated by the calculation means coincides with a predetermined value; and imbalance detection means for detecting an air-fuel ratio imbalance between the plurality of cylinders based on a reduction amount of fuel injection amount, the reduction amount being provided by control that is exercised for each of the plurality of cylinders by the injection amount control means, wherein means for calculating the reduction amount of fuel injection amount due to the control by the injection amount control means for each of the plurality of cylinder; means for acquiring a calculated value of an air-fuel ratio for the target cylinder based on the reduction amount of fuel injection amount, the calculated value of the air fuel ratio being an air fuel ratio of the target cylinder before the target cylinder is controlled by the injection amount control means; means for detecting an air-fuel ratio imbalance between the plurality of cylinders based on a comparison of the calculated values of the air-fuel ratios between the plurality of cylinders, and wherein the combustion parameter is at least one of quantities selected from a group of an in-cylinder pressure, internal energy, indicated torque, indicated work, a burning velocity, and the amount of generated heat, or a physical quantity correlated with at least one of the quantities selected from the group.