A waterproof structure for a casing has a first casing, a second casing to be put together with the first casing, and a waterproof member formed of an elastic material to prevent water from penetrating between the first casing and the second casing. The second casing has a recess. The waterproof member has a peripheral part which, when fitted into the recess, prevents penetration of water. The peripheral part is provided at the periphery of the waterproof member, which is laid out all around space between the first casing and the second casing. A projection engages with a dent. A restriction part of the first casing, provided at a position facing the peripheral part and protruding toward the second casing, prevents the peripheral part from coming out.