An electronic component unit (10) applied to a wire harness (WH) includes a power supply terminal (11) that is connected to a power supply (B2) mounted on a vehicle (V) and capable of supplying power at a first voltage (V1), a circuit branch portion (13) that is connected to the power supply terminal (11) to branch power supplied from the power supply (B2) into a plurality of power supply systems (PL), and a voltage converter (15) that is detachably provided from at least one of the plurality of power supply systems (PL) in the circuit branch portion (13), and converts a voltage of the power supplied from the power supply (B2) into a second voltage (V2) lower than the first voltage (V1) to output the second voltage (V2).
