A power supply control apparatus configured to detect a failure of a semiconductor switch element in a switching circuit, the switching circuit including a plurality of semiconductor series circuits which are connected in parallel to one another, and each of the semiconductor series circuits having a plurality of semiconductor switch elements (FET1 to FET6) which are connected in series with reverse polarities, the power supply control apparatus comprising: a reference resistance value storing unit that stores in advance information on a combined resistance value between an input and an output of the switching circuit in a reference state as a reference resistance value (Rref) of a combined resistance value in the entire circuit between the input side and the output side of the switching circuit in the ON state in which all of the semiconductor switch elements (FET1 to FET6) are conductive; a conduction current detection unit configured to detect a magnitude of a current flowing through an entire of the switching circuit as a conduction current; a potential difference detection unit configured to detect a potential difference between the input and the output of the switching circuit as an input-output potential difference; a voltage drop calculation unit configured to calculate an assumed voltage drop based on the reference resistance value and the conduction current detected by the conduction current detection unit; a voltage comparison unit configured to compare the input-output potential difference detected by the potential difference detection unit with the assumed voltage drop calculated by the voltage drop calculation unit; and a failure identification unit configured to identify a presence or absence of a failure of the semiconductor switch element based on a comparison result of the voltage comparison unit. a reference resistance value storing unit that stores in advance information on a combined resistance value between an input and an output of the switching circuit in a reference state as a reference resistance value (Rref) of a combined resistance value in the entire circuit between the input side and the output side of the switching circuit in the ON state in which all of the semiconductor switch elements (FET1 to FET6) are conductive; a conduction current detection unit configured to detect a magnitude of a current flowing through an entire of the switching circuit as a conduction current; a potential difference detection unit configured to detect a potential difference between the input and the output of the switching circuit as an input-output potential difference; a voltage drop calculation unit configured to calculate an assumed voltage drop based on the reference resistance value and the conduction current detected by the conduction current detection unit; a voltage comparison unit configured to compare the input-output potential difference detected by the potential difference detection unit with the assumed voltage drop calculated by the voltage drop calculation unit; and a failure identification unit configured to identify a presence or absence of a failure of the semiconductor switch element based on a comparison result of the voltage comparison unit.