To provide a high-power-factor motor controller which can drive a synchronous motor with less vibration and low noise even for large load torque variations, and can suppress a direct current voltage increase due to regenerative energy.

In a motor controller 10, a reference value calculation section 29 calculates a first reference value corresponding to amplitude of a motor voltage on the basis of a phase difference between the motor voltage and a motor current flowing through a stator of a synchronous motor 2. A correction section 24 compares a line voltage between DC wiring HL and LL and a predetermined upper limit value, and outputs a second reference value that is a value obtained by adding a correction value according to the dimension of a load torgue to the first reference value when the line voltage is the upper limit value or less, and outputs a third reference value that is a value obtained by adding the correction value after being subjected to reduction to the first reference value when the line voltage exceeds the upper limit value. A control signal generation section 25 generates a control signal for controlling an inverter device 12 on the basis of the second or third reference value outputted from the correction section.