The present invention addresses the problem of obtaining an electronic control device for a vehicular automatic transmission that suppresses sudden acceleration, sudden deceleration, and gear shift shock that occur when the transmission moves into a fail-safe mode due to the electronic control device stopping during a main CPU abnormality. An electronic control device 100 for a vehicular automatic transmission has: a main CPU 3 that performs gear shift control for the vehicular automatic transmission; and a sub-CPU 4 that detects abnormalities in the main CPU 3. When the sub-CPU 4 detects an abnormality in the main CPU 3 while the vehicle is traveling, the sub-CPU 4 stops the gear shift control executed by the main CPU 3.