To provide attaching structure of a fan case allowing simple and sure attachment of a fan case equipped with a cooling fan to a unit, even with narrow a space around a unit inside a board.

In this attaching structure of a fan case 4, the fan case 4 equipped with a cooling fan 3 is attached to the top face of a unit arranged inside a board 1 having a ventilation hole 2a. An engagement hole 2b is formed adjacent to the deep side of the board 1 of the ventilation hole 2a formed on the top face of the unit 2, and a projection piece 2c is disposed at the edge on the deep side of the engagement hole 2b. A tongue piece 4a is disposed at the position corresponding to the engagement hole 2b of the fan case 4, and the tongue piece 4a of the fan case 4 is engaged with the engagement hole 2b of the unit 2.