A communication interface apparatus is provided for extending a communication available distance, suppressing the influence of a power receiving circuit on a transmitter/receiver circuit (3), and reducing the cost. The transmitter/receiver circuit is configured in a balanced circuit to enhance the driving capability, so that a sufficient amplitude can be ensured even if a power receiving circuit (8) provides a low received voltage. A low pass filter (LPF) is added in front of the power receiving circuit to eliminate electrical interference between the power receiving circuit and the transmitter/receiver circuit, resulting in improved input impedance frequency characteristics of the power receiving circuit. The LPF is connected to both plus and minus terminals of the power receiving circuit, and bypass capacitor is shared by plus and minus inputs, thereby providing well balanced operation characteristic. A Zener diode may be utilized in the LPF to form a two-stage stabilizing circuit, so that an IC-based voltage regulator can be used even with a high input voltage provided from if the power receiving circuit.