A control device capable of accurately detecting a rotor rotation angle is provided. The control device includes variable resistors R1 to R4 for converting the currents flowing in the four-phase coils of the current detection resolver into voltages, two differential amplifiers for a first phase signal of the voltage difference between the detection voltages of the variable resistors R1 and R3, and a second phase signal of the voltage difference between the detection voltages of the variable resistors R2 and R4 respectively, two phase shifters for shifting the phase of the first phase signal and the second phase signal respectively, a synthesizer for a phase modulation signal by synthesizing the phase shifted first phase signal and the phase shifted second phase signal, and an adjuster for adjusting the resistance values of the variable resistors R1 to R4 based on the width of the envelope of the phase modulation signal.