A control apparatus for an internal combustion engine, includes: a crankshaft; a crank angle detection unit; a generator; and a control unit to which alternating voltage signals are input, that ascertains ignition timings based on crank signals, performs ignition control so as to spark the internal combustion engine at the ignition timings, performs polarity determination processing in which the control unit determines a polarity of the alternating voltage signal each predetermined cycle and determines a current polarity determination result, and performs reverse rotation detection processing in which the control unit obtains the current polarity determination result each time the crank signal is detected so that the control unit ascertains a polarity cycle of the alternating voltage signals and in which the control unit determines that the crankshaft is in reverse rotation and stops the ignition control.