An electronic control device comprising: at least two pairs of detection means (5a,5b) each of which is a rotation angle sensor configured to detect a rotation angle of a motor of an electric power steering device; and a control portion configured to control the motor by using information about these detection means (5a,5b) and which includes abnormality determination means configured to perform determination as to abnormality of the detection means (5a,5b), the control portion being configured to continue control with a normal one of the pairs at a time of an abnormality, wherein the control portion is further configured to execute control on one of the pairs of detection means (5a,5b), the abnormality determination means is further configured to perform, for the execution, detection of abnormality at a normal speed and performs detection of abnormality of the other of the pairs at a speed not higher than the normal speed, the normal speed corresponding to a cycle of information acquisition, in a case where a sign of abnormality of the detection means (5a, 5b) at the normal speed is detected, the control portion is further configured to perform switching to the other normal pair and continues the control, and the abnormality determination means is further configured to perform detection of abnormality of the other normal pair at the normal speed, and meanwhile, to continue performing detection of abnormality of the abnormal pair at a speed not higher than the normal speed, and once performing switching to the normal pair, the control portion is further configured to neither perform switching again within a predetermined time period even if a sign of abnormality of the normal pair is detected within the predetermined time period, nor perform switching again within the predetermined time period even if the abnormal pair is determined to be normal. at least two pairs of detection means (5a,5b) each of which is a rotation angle sensor configured to detect a rotation angle of a motor of an electric power steering device; and a control portion configured to control the motor by using information about these detection means (5a,5b) and which includes abnormality determination means configured to perform determination as to abnormality of the detection means (5a,5b), the control portion being configured to continue control with a normal one of the pairs at a time of an abnormality, wherein the control portion is further configured to execute control on one of the pairs of detection means (5a,5b), the abnormality determination means is further configured to perform, for the execution, detection of abnormality at a normal speed and performs detection of abnormality of the other of the pairs at a speed not higher than the normal speed, the normal speed corresponding to a cycle of information acquisition, in a case where a sign of abnormality of the detection means (5a, 5b) at the normal speed is detected, the control portion is further configured to perform switching to the other normal pair and continues the control, and the abnormality determination means is further configured to perform detection of abnormality of the other normal pair at the normal speed, and meanwhile, to continue performing detection of abnormality of the abnormal pair at a speed not higher than the normal speed, and once performing switching to the normal pair, the control portion is further configured to neither perform switching again within a predetermined time period even if a sign of abnormality of the normal pair is detected within the predetermined time period, nor perform switching again within the predetermined time period even if the abnormal pair is determined to be normal.