A bidirectional interface circuit includes a first current mirror circuit that copies a first reference current to generate a first current sunk from a first output terminal, a second current mirror circuit that copies a second reference current to generate a second current sunk from a second output terminal, an interception switch that is connected between the first output terminal and the second output terminal, a first comparator that outputs an upper state signal based on a comparison result of a voltage of the first output terminal and a first threshold voltage, a third current mirror circuit that copies one of a third reference current and a fourth reference current to supply a third current flowing to a third output terminal, and a second comparator that outputs a lower state signal based on a comparison result of a voltage of the second output terminal and a second threshold voltage.