To provide a structure of water-proof structure in which function buttons are placed on a side of the case at which operation is made easy without the need for the use of any special non-slip rubber to an outer face of the case.

An endless seal rubber 3 is interposed between a case cover 2 and a opening of a case 1 into which a printed circuit board with function elements mounted thereon is built to attain the water-proof structure for the case. In this case, an outer side 3b of the endless seal rubber 3 is swollen to the outside from the outer side between the case 1 and the case cover 2 so as to act as a non-slip rubber, and at least one of function buttons 13, 14, 26 operated by a finger tip is integrally formed to part of the outside of the endless seal rubber 3. Moreover, electric switches 17, 18, 28 are fixed to a surrounding part of the printed circuit board 7 corresponding to the function buttons 13, 14, 26 and inner depressing knobs 16, 27 in the endless seal rubber 3 operated elastically by the function buttons 13, 14, 26 are faced to the operation parts of the electric switches 17, 18.