A motor controller includes, in a microcomputer, a voltage fall determiner determining whether a reference voltage falls from a normal value based on an Analog-to-Digital (A/D) conversion value of a second voltage from an A/D converter, and a corrector (i) calculating a correction coefficient based on the A/D conversion value of the second voltage from the A/D converter and (ii) correcting an A/D conversion value of an input voltage that is output from the A/D converter. A core of the microcomputer generates a control signal based on an input voltage A/D conversion value, when the voltage fall determiner determines that the reference voltage is equal to or higher than a normal reference value. The motor controller keeps its motor control accuracy in such manner, even when a fall of an A/D conversion reference voltage is observed.