To provide a waterproof structure of a case, capable of making its workability good in assembling while maintaining the waterproof effect.

In the waterproof structure of the case, a storage recess part 27 for storing a waterproof packing 50 is disposed around a through-hole 26 of the case 20, and a planar flange part 41B which includes an operation recess part 41A for rotating/fastening a screw body 40 by using a tool, is disposed at the screw head 41 of the screw body 40, and the waterproof packing 50 is attached to and held by a shaft part 42 of the screw body 40 which is continuously formed with the flange part 41B. The case 20 and a support member (case 10) are concurrently fastened and fixed by the screw body 40 in such the state that the waterproof packing 50 is in its compressed shape between inner circumferential walls 27A, 27B of the storage recess part 27 disposed at the case 20 and the flange part 41B/the shaft part 42 of the screw body 40, when screwing the screw body 40 to which the waterproof packing 50 is attached and held.