A case locking device is provided. For example, an outer case and an inner case used for various types of electronic devices, such as set-top boxes (STB), are connected by a lock using a resilient force from an elastic material, such as a spring, so that the outer case and the inner case may be separated from each other using only a separately provided jig. Accordingly, the outer case and the inner case may be connected to each other more easily and any general user may be prevented from separating the case arbitrarily, thus making it possible to effectively prevent catastrophic failures from occurring at the electronic device due to a user's arbitrary manipulation.