In a rotation angle detection device for detecting a rotation angle and a rotation speed of a motor generator by using a resolver, a resolver detection accuracy is improved by raising the amplitude or frequency of an excitation signal when the motor generator is performing a driving operation. Furthermore, by reducing the amplitude or frequency of the excitation signal when the motor generator is not performing a driving operation, it is possible to suppress the amount of heat generated by the excitation circuit and the resolver, while maintaining a resolver detection accuracy that enables information about the rotation speed of the motor generator to be obtained.