An on-vehicle charging apparatus charges a battery mounted on the vehicle. In the apparatus, a generator generates electric power to output voltage for charging the battery and a controller, which is located outside the generator, outputs a pulse signal for controlling a generated state of the generator. A reception device receives the pulse signal outputted from the controller. The received signal is subjected to filtering at a filter, where pulse signals whose cycles are different from a predetermined cycle are removed. Further, using the outputted pulse signal from the filter, a duty ratio of the pulse signal is calculated. A voltage outputted from the generator is regulated based on the calculated duty ratio.