An electronic control device includes: an accommodation element; a cover element; a connection element for fixing the cover element to the accommodation element; an extending protrusion extending and protruding to an outside from a contact portion between the cover element and the accommodation element; and a control element formed in the accommodation space. The extending protrusion includes a protrusion portion, which protrudes toward a bottom side or a cover element side and is formed to cover the contact portion. A clearance having predetermined dimensions is formed between the protrusion portion and one of an outer wall of the cover element and an outer wall of the accommodation element, which is near the contact portion.