To provide a motor controller capable of properly driving a motor using an accurately estimated rotation angle, when a rotation angle detecting means fails, without causing significant increase.

In a normal state in which there is no failure occurring in a resolver 2, a motor 1 is controlled using a detected rotation angle S detected by the resolver 2. If a failure occurs in the resolver 2, the motor 1 is controlled by using an estimated rotation angle E calculated by a rotation angle estimating section 31. When the resolver 2 in a normal state, a detected induction voltage ES from a rotation angle speed obtained from the detected rotation angle S. An estimated induced voltage EE is calculated, based on a two-phase voltage command value V and a two-phase detection current I. Based on the comparison of these voltages, a correction value C for correcting the estimated induction voltage EE is generated and is written in a corrected value storage section 30. The rotation angle estimating section 31 corrects the estimated induction voltage EE by the correcting value C, and an estimated rotation angle E is obtained by using the corrected estimated induced voltage.