Abstract: A rotation angle measuring apparatus comprises a throttle valve for controlling the amount of air flow of an internal combustion engine, a throttle sensor coupled to a rotation shaft of the throttle valve, and a logic circuit which includes absolute rotation angle detecting means for receiving an output signal of the throttle sensor to produce an absolute signal, forward/reverse rotation direction discriminating means for receiving an output signal of the throttle sensor to produce a direction signal, and an up/down counter for receiving the absolute signal, the direction signal and a count signal outputted from the forward/reverse rotation direction discriminating means to output a signal representative of a rotation position of the rotation shaft of the throttle valve.