To control a motor without interruption even though a signal line from a resolver to a controller body is broken or short-circuited.

A clock output unit 24 of the controller body 20 outputs a clock signal S1 in synchronization with a triangular wave. A synchronous excitation signal formation circuit 6 low-pass filters the clock signal S1 and outputs an excitation reference signal S2 to the resolver 2. A data formation unit 25 generates a cosine-wave amplitude signal Lc and a sine-wave amplitude signal Ls from a cosine signal S3 and a sine signal S4 from the resolver 2. A first rotation angle detecting means 29 computes a first rotation angle 1 using the cosine-wave amplitude signal Lc. A second rotation angle detecting means 30 computes a second rotation angle 2 using the sine-wave amplitude signal Ls. A third rotation angle detecting means 31 computes a third rotation angle 3 using the cosine-wave amplitude signal Lc and the sine-wave amplitude signal Ls. Any anomaly is detected from the individual rotation angles to select a normal rotation angle .