In industrial plants, straight-line horizontal pipe is typically arranged along with vertical pipe, curved pipe, valves, and flanges. So, it is hoped that the robot can automatically inspect along the pipe. In this paper, we propose the structure of a pipe-surface inspection robot with omnidirectional mobile mechanism. The robot consists of the lower unit and the upper unit. The lower unit has six leg-wheel units that consist of the drive part, the lift part and a magnetic wheel. The upper unit has the differential gear unit and the drive joint that enable a steering, a swing and a bending motion.