A direct-current power supply circuit, incorporated in an IC card, includes a coil for receiving an amplitude-modulated signal from an external device through electromagnetic induction. A full-wave rectifying circuit rectifies the amplitude-modulated signal received by the coil. The rectified output signal is used to charge a smoothing capacitor. A clamp circuit controls the terminal voltage of the smoothing capacitor to a predetermined level so as to produce a power supply voltage. The clamp circuit controls an output transistor to stabilize the power supply voltage to a constant level. Furthermore, the direct-current power supply circuit includes a short-circuit preventing circuit to forcibly turn off the output transistor when the electric potential difference between both ends of the coil is smaller than a predetermined value, thereby preventing the power supply voltage from suddenly decreasing due to delay of operation of the circuit elements when the coil output becomes zero due to amplitude modulation.