A casing 1, a terminal plate 30 that is exchangeably mountable in an opening 23 formed in the casing 1; and a water sealing component 50 disposed around a terminal 31 formed on the terminal plate 30, are provided. A flange 24 is formed inside the opening 23 so as to surround a center of the opening and project toward the center of the opening. When the terminal plate 30 is mounted on the flange 24, an outer side surface of the terminal plate 30 is flush with a surface 21 of the casing in a portion where the opening is formed. With this structure, an electronic device can be obtained that is reliably waterproof and/or dustproof in a connection terminal portion that is exchangeable so as to enhance an expandability.