To provide a motor controller capable of reducing an electric power consumption while ensuring suitable motor operation.

A motor controller 27 includes: a driving circuit 40 for supplying a three-phase AC voltage to a motor 21; a micro computer 41 for controlling the drive of the motor 21 through the driving circuit 40; and a pre-driver circuit 48 for amplifying a PWM drive signal output from the micro computer 41. Furthermore, the motor controller 27 includes a motor rotational angle sensor dedicated input/output signal generating circuit 43 for outputting an excitation signal of a motor rotational angle sensor 22 and receiving an output signal of the motor rotational angle sensor 22 as an input signal. Here, a relay 46 is provided so that it switches on and off the supply of electric power to the motor rotational angle sensor dedicated input/output signal generating circuit 43. Then, if it is not necessary to drive the motor 21, the micro computer 41 allows the relay 46 to switch off the electric power supply to the motor rotational angle sensor dedicated input/output signal generating circuit 43.