The present invention provides an electronic control unit which is capable of suppressing harmful effects caused by liquid while suppressing increase in the size thereof. The electronic control unit includes an electronic component in which a circuit element coated with an anti-splash agent is implemented, a casing, and a liquid discharge portion. The casing includes a base on which the electronic component is mounted, a cover which is connected to the base in the state where the electronic component is covered with the cover, and a connector which electrically connects the electronic component to the outside. The liquid discharge portion includes a flow passage in which liquid which has intruded into an internal space in the casing formed by the base, the cover and the connector for housing the electronic component flows, and an opening portion which discharges the liquid to the outside of the internal space via the flow passage.