To provide an overcurrent protection circuit capable of preventing overcurrent, even when one end of a current detecting resistor element becomes open, and to provide an on-vehicle electronic apparatus.

The overcurrent protection circuit includes a current value determination part for determining whether a current value of a current inputted from an input part 29 lies within a predetermined range, based on voltage reduction in a current detecting resistor element 6, and a state determination part for determining whether the voltage of a power supply 11 for applying a current to the input part 29 is a predetermined voltage. A control part, when the current value determination part determines that the current value of the current inputted from the input part 29 does not lie within the predetermined range and the state determination part determines that the voltage of the power supply 11 is in the predetermined voltage, it is determined that the current-detecting resistor element 6 is in a short-circuited or an open state and restricts or interrupts conversion in a voltage conversion part.