A position detecting device for a motor includes a resolver, amplifiers and a microcomputer. The microcomputer corrects an amplified sine wave signal to have the same amplitude in both positive and negative polarities, and corrects an amplified cosine wave signal to have the same amplitude in both positive and negative polarities. The microcomputer further corrects the corrected sine wave signal or the corrected cosine wave signal to have the same amplitude therebetween. The rotation position is determined accurately based on the sine wave signal and the cosine wave signal of the same amplitude, even if the amplifiers have different operation characteristics.