An internal combustion engine, which includes a collection device that is arranged in an exhaust pipe through which an exhaust gas emitted from a cylinder passes and collects PM contained in the exhaust gas and an NOx sensor that is arranged on an upstream side of the collection device and detects an NOx content in the exhaust gas, includes: an estimating device which estimates a PM content in the exhaust gas at the upstream side of the collection device from a detection value of the NOx sensor, based on a trade-off relation between an NOx emission amount and a PM emission amount from the cylinder.