To provide an electronic control device capable of favorably reducing operation loads even in a case of executing a plurality of different kinds of control such as normal engine control, control related to troubleshooting in a fuel vapor processing system, etc.

In this device, a plurality of programs for respective functions including commonly usable programs are stored in a single program memory for a normal mode related to operation control of an on-vehicle engine and leak diagnosis mode related to troubleshooting of a fuel vapor processing system automatically executed after stop of operation of the engine. In a reference table including link information for programs separately provided to be respectively required for the two control modes, necessary programs for each control mode are preliminarily related to be extracted. As the control mode is specified, the programs related to the specified control mode only are executed in order.