ELECTRONIC UNIT MOUNTING STRUCTURE

PROBLEM TO BE SOLVED: To provide an electronic unit mounting structure which has a simple structure and can be downsized.SOLUTION: An electronic unit mounting structure 1 is a structure for mounting an electronic unit 3 on an upper surface 40a of a case 4 of an electric connection box 2. A case 5 of the electronic unit 3 includes: a case body 50; a projection part 51 projecting from one side surface 50c of the case body 50; and a lock part 52 which is provided on another side surface 50d. The case 4 of the electric connection box 2 includes: a vertical wall 61 extending in a direction orthogonal to the upper surface 40a; a horizontal wall 64 projecting from the vertical wall 61 to the electronic unit 3 side; a projection part housing space 66 extending from the horizontal wall 64 to a lower side of the upper surface 40a; and a lock reception part 42. The projection part 51 is inserted into the projection part housing space 66 and the electronic unit 3 is rotated. With this, the projection part 51 is brought into contact with the horizontal wall 64, the lock part 52 is engaged with the lock reception part 42 and the electronic unit 3 is mounted on the upper surface 40a of the case 4 of the electric connection box 2.