This paper describes the running static analysis of an in-pipe mobile robot using a wheel drive mechanism for straight piping. The wheel mechanism, which is driven by planetary gears and worm gears, can both drive the wheels and press them against the pipe wall using only an actuator and simple mechanisms. The relation among the size of the load, carrier angle, and the pressing load against the pipe wall is theoretically analyzed and experimentally examined. The traction force of the robot is calculable with motor driving torque, and the maximum traction force is estimated with no-load driving torque of robot and torque constant of the motor. From the running experiments by the prototype robot, which is 45 mm in diameter and 130 mm in length, the maximum traction force was at least 20 times the weight of the robot.