A casing device and an insertion structure thereof are provided. The casing device includes a first casing, a second casing, and an insertion structure. The second casing has an engagement structure. The insertion structure includes a tamperproof element. The tamperproof element has one end extended outward to form two barb-like protruding portions and the other end protrudingly provided with a leaf spring. The leaf spring includes resilient protruding plates protrudingly formed on the outer surface of the tamperproof element. Since the resilient protruding plates and the engagement structure are engaged with each other, the insertion structures can clamp the first casing and the second casing to prevent consumers from dismantling an electronic device enclosed by the casing device but enable the electronic device manufacturers to confirm whether the casing device has been inappropriately dismantled by the consumers, thereby settling disputes over damages liability between a consumer and a manufacturer.