An abnormality determination apparatus for an internal combustion engine in which an intake passage upstream of a supercharger and a crankcase are connected by a breather line includes: an intake flow rate detection unit that detects an intake flow rate in the intake passage; and an abnormality determination unit that determines abnormality of the breather line. The abnormality determination unit calculates a rotation second-order component of a fluctuation waveform of the intake flow rate, accumulates a first number of times for which the rotation second-order component exceeds an upper threshold and a second number of times for which the rotation second-order component falls below a lower threshold, and determines the abnormality of the breather line by comparing an accumulated value of the first number of times and the second number of times with the number of revolutions of a crank.