A variety of applications that are accessible through app markets provide useful features and functions. However, those applications can present many GUI bugs due to the deficiency of testing processes. Even though various approaches have been developed for mobile app testing, GUI bugs in applications are still difficult to be identified due to the absence of efficiency, lack of automation, and necessity of access to the source code. In this paper, we propose an automated black-box testing method for efficient GUI bug detection. Our experimental results show that the proposed method achieves better code coverage and uncovers GUI bugs when compared with existing black-box testing called Monkey.