An electronic control device comprising: - a circuit board mounted with an electronic component; - a case body, - a lid cover mounting part serving as an opening is formed at one end, and upper and lower guide rails (13A, 13B) forming a guide groove for inserting the circuit board are included on each internal side surface; and - a lid cover for closing an open surface of the lid cover mounting part, the circuit board being held by the guide groove formed in an internal space of the case body, wherein - an elastically deformable engaging part (19, 31A, 31B) is provided at the circuit board or the case body, an engaged part (21, 33A, 33B) for complementarily engaging with the engaging part (19, 31A, 31B) is provided at the circuit board or the case body, the engaging part (19, 31A, 31B) is deformed when the circuit board is slid and housed in the guide groove formed inside the case body, and the engaging part (19, 31A, 31B) is configured to engage with the engaged part (21, 33A, 33B) formed at the circuit board or the case body when the circuit board reaches a predetermined position, wherein the engaging part (19, 31A, 31B) is integrally formed with each side of the lid cover, the lid cover and the circuit board are integrally configured, and when the circuit board is inserted into the guide groove and reaches the predetermined position, the engaging part (19, 31A, 31B) is configured to engage with a locking part (21, 33A, 33B) serving as the engaged part (21, 33A, 33B) formed at the guide rail (13A, 13B), the electronic control device is characterized in that - a connector mounting part is formed at another end of the case body than the end where the lid cover mounting part is formed, - a board reception part (16, 24A) for preventing movement of the circuit board to the connector mounting part side is formed in a vicinity of the connector mounting part, - a step part (17, 23A) is formed at each side end part of the circuit board on a side opposite to a part of the circuit board fixed to the lid cover, and movement of the circuit board is regulated by butting the step part (17, 23A) against the board reception part (16, 24A), wherein a position of the engaged part is the position at which the step part formed at each side end part of the circuit board is butted against the board reception part. - a circuit board mounted with an electronic component; - a case body, - a lid cover mounting part serving as an opening is formed at one end, and upper and lower guide rails (13A, 13B) forming a guide groove for inserting the circuit board are included on each internal side surface; and - a lid cover for closing an open surface of the lid cover mounting part, the circuit board being held by the guide groove formed in an internal space of the case body, wherein - an elastically deformable engaging part (19, 31A, 31B) is provided at the circuit board or the case body, an engaged part (21, 33A, 33B) for complementarily engaging with the engaging part (19, 31A, 31B) is provided at the circuit board or the case body, the engaging part (19, 31A, 31B) is deformed when the circuit board is slid and housed in the guide groove formed inside the case body, and the engaging part (19, 31A, 31B) is configured to engage with the engaged part (21, 33A, 33B) formed at the circuit board or the case body when the circuit board reaches a predetermined position, wherein the engaging part (19, 31A, 31B) is integrally formed with each side of the lid cover, the lid cover and the circuit board are integrally configured, and when the circuit board is inserted into the guide groove and reaches the predetermined position, the engaging part (19, 31A, 31B) is configured to engage with a locking part (21, 33A, 33B) serving as the engaged part (21, 33A, 33B) formed at the guide rail (13A, 13B), the electronic control device is characterized in that - a connector mounting part is formed at another end of the case body than the end where the lid cover mounting part is formed, - a board reception part (16, 24A) for preventing movement of the circuit board to the connector mounting part side is formed in a vicinity of the connector mounting part, - a step part (17, 23A) is formed at each side end part of the circuit board on a side opposite to a part of the circuit board fixed to the lid cover, and movement of the circuit board is regulated by butting the step part (17, 23A) against the board reception part (16, 24A), wherein a position of the engaged part is the position at which the step part formed at each side end part of the circuit board is butted against the board reception part.