The present invention relates to a motor controller of an air conditioner, including an inverter including a plurality of switching elements and adapted to convert a DC voltage, input through switching operations of the switching elements, into an AC voltage and supply the converted voltage to a motor, a power calculation unit that calculates electric power applied to the motor, an angle calculation unit that calculates an optimal phase angle of a current command value based on the calculated electric power; and a microcomputer that outputs a switching control signal to control the switching elements of the inverter based on the optimal phase angle.