To provide an inexpensive vehicle overcurrent detector with a small and easily manufactured constitution.

The vehicle overcurrent detector includes a substrate 10, an FET bare chip 20 which is placed on the substrate 10 and is arranged on a power supply line of an on-vehicle device OBU, a potential difference detection circuit 32 having two input electrodes 35 and 36 and detecting a potential difference of currents flowing in and out of the FET bare chip, a current value calculating circuit 33 converting the potential difference detected by the potential difference detecting circuit into a current value, a first bonding wire 41 connecting a drain electrode 21 of the FET bare chip and one input electrode 35 of the potential difference detecting circuit, and a second bonding wire 42 connecting one input electrode 35 of the potential difference detection circuit and the other input electrode 36 of the potential difference detection circuit.