An electronic control unit diagnoses a short failure of an inverter FETs and diagnoses whether the failure of the FET-short detecting section has occurred. The unit controls a motor through an inverter including a bridge having an upper-stage FETs and a lower-stage FETs via an MCU, having: an FET-short detecting section to detect a short failure of the upper-stage FETs and the lower-stage FETs based on respective connection point voltages of the upper-stage FETs and the lower-stage FETs; and a diagnostic function to detect a failure of the FET-short detecting section. The diagnostic function diagnoses the failure of the FET-short detecting section at start up and turns-OFF the upper-stage FETs and the lower-stage FETs when the failure is detected. The FET-short detecting section diagnoses the short failure of the upper-stage FETs and the lower-stage FETs when the failure of the FET-short detecting section is not detected.