The assembling performance of an electronic control device can be improved. An electronic control device includes a control board 12 and a power source conversion board 13. The control board 12 includes a first power source terminal 15, a first GND terminal 16, and a male floating connector 17 on one surface. The power source conversion board 13 includes a second power source gripping terminal 18 electrically connected to the first power source terminal 15, a second GND gripping terminal 19 electrically connected to the first GND terminal 16, and a female floating connector 20 electrically connected to a male floating connector 17 on one surface.