An in-vehicle electronic control device for diagnosing the details of an abnormality of a microcomputer appropriately is provided. A monitoring function for detecting a malfunction by monitoring input/output of a main function of a hardware part and a monitoring function for detecting an abnormality by monitoring the calculating result of a main function in a software part are provided in a microcomputer. The main function to be monitored is implemented with a different structure than the malfunction/abnormality monitoring function. Furthermore, a malfunction processing circuit for monitoring an abnormality of the microcomputer is provided outside the microcomputer.