An alternator control apparatus, comprising: a first controller that is adapted to control an alternator; and a second controller that is adapted to periodically transmit an instruction signal to the first controller, the instruction signal being related to electric power generation of the alternator, wherein the instruction signal selectively includes a power generation instruction signal that causes a power generated state of the alternator, and a non-power generation instruction signal that causes a non-power generated state or a power generation suppressed state of the alternator, wherein the first controller is adapted to, if a detection value of a power supply voltage is less than a predetermined threshold and the first controller receives the power generation instruction signal from the second controller, control a power generation amount of the alternator such that the power generation amount is greater than a predetermined reference, and, if the detection value of the power supply voltage is less than the predetermined threshold and the first controller receives the non-power generation instruction signal from the second controller, form or maintain the non-power generated state or the power generation suppressed state of the alternator according to the non-power generation instruction signal, characterized in that the second controller is adapted to periodically transmit the non-power generation instruction signal to the first controller until the detection value of the power supply voltage becomes greater than or equal to the predetermined threshold after a completion of an engine start. a first controller that is adapted to control an alternator; and a second controller that is adapted to periodically transmit an instruction signal to the first controller, the instruction signal being related to electric power generation of the alternator, wherein the instruction signal selectively includes a power generation instruction signal that causes a power generated state of the alternator, and a non-power generation instruction signal that causes a non-power generated state or a power generation suppressed state of the alternator, wherein the first controller is adapted to, if a detection value of a power supply voltage is less than a predetermined threshold and the first controller receives the power generation instruction signal from the second controller, control a power generation amount of the alternator such that the power generation amount is greater than a predetermined reference, and, if the detection value of the power supply voltage is less than the predetermined threshold and the first controller receives the non-power generation instruction signal from the second controller, form or maintain the non-power generated state or the power generation suppressed state of the alternator according to the non-power generation instruction signal, characterized in that the second controller is adapted to periodically transmit the non-power generation instruction signal to the first controller until the detection value of the power supply voltage becomes greater than or equal to the predetermined threshold after a completion of an engine start.