A sensorless motor control device that controls a brushless DC motor by pulse width modulation using an inverter circuit, the motor control device comprising: a ripple current estimating device configured to estimate a magnitude of a ripple current based on current flowing through a drive power supply line of the inverter circuit; and a control device (13, 14), wherein: the inverter circuit includes a first output terminal and a second output terminal respectively corresponding to two energizing phases of the inverter circuit; the inverter circuit is connected between the brushless DC motor and a drive power supply via said power supply line; the first output terminal of the inverter circuit corresponds to one of the energizing phases of the brushless DC motor; and the second output terminal of the inverter circuit corresponds to another one of the energizing phases of the brushless DC motor; when the magnitude of the ripple current is less than or equal to a threshold value, the control device (13, 14) performs balanced-drive switching that the first output terminal is repeatedly and alternately connected to a high voltage side and a low voltage side of the drive power supply, and the second output terminal, in an opposite way of the first output terminal, is repeatedly and alternately connected to the low voltage side and the high voltage side of the drive power supply; and when the magnitude of the ripple current exceeds the threshold value, the control device (13, 14) performs unbalanced-drive switching that the first output terminal is repeatedly and alternately connected to the high voltage side and the low voltage side, and the second output terminal is connected only to the low voltage side. a ripple current estimating device configured to estimate a magnitude of a ripple current based on current flowing through a drive power supply line of the inverter circuit; and a control device (13, 14), wherein: the inverter circuit includes a first output terminal and a second output terminal respectively corresponding to two energizing phases of the inverter circuit; the inverter circuit is connected between the brushless DC motor and a drive power supply via said power supply line; the first output terminal of the inverter circuit corresponds to one of the energizing phases of the brushless DC motor; and the second output terminal of the inverter circuit corresponds to another one of the energizing phases of the brushless DC motor; when the magnitude of the ripple current is less than or equal to a threshold value, the control device (13, 14) performs balanced-drive switching that the first output terminal is repeatedly and alternately connected to a high voltage side and a low voltage side of the drive power supply, and the second output terminal, in an opposite way of the first output terminal, is repeatedly and alternately connected to the low voltage side and the high voltage side of the drive power supply; and when the magnitude of the ripple current exceeds the threshold value, the control device (13, 14) performs unbalanced-drive switching that the first output terminal is repeatedly and alternately connected to the high voltage side and the low voltage side, and the second output terminal is connected only to the low voltage side. the inverter circuit includes a first output terminal and a second output terminal respectively corresponding to two energizing phases of the inverter circuit; the inverter circuit is connected between the brushless DC motor and a drive power supply via said power supply line; the first output terminal of the inverter circuit corresponds to one of the energizing phases of the brushless DC motor; and the second output terminal of the inverter circuit corresponds to another one of the energizing phases of the brushless DC motor; when the magnitude of the ripple current is less than or equal to a threshold value, the control device (13, 14) performs balanced-drive switching that the first output terminal is repeatedly and alternately connected to a high voltage side and a low voltage side of the drive power supply, and the second output terminal, in an opposite way of the first output terminal, is repeatedly and alternately connected to the low voltage side and the high voltage side of the drive power supply; and when the magnitude of the ripple current exceeds the threshold value, the control device (13, 14) performs unbalanced-drive switching that the first output terminal is repeatedly and alternately connected to the high voltage side and the low voltage side, and the second output terminal is connected only to the low voltage side.