In this paper, we propose a crawling motion to reduce the risk of malfunction due to falling when a legged robot travels across rough terrain. This locomotion method includes a phase in which the torso of the robot comes into contact with the ground to lower its center of mass compared with that during conventional bipedal or quadrupedal walking motion. In rough terrain, the ability of a robot to crawl is very likely to be hindered since its feet may encounter holes or protrusions caused by road surface damage. To avoid this issue, we suggest a modified foot trajectory control method based on information obtained by force and attitude angle sensors. To verify the effectiveness of the proposed crawling motion on rough terrain, we created a terrain model using a dynamics simulator and conducted an experiment by applying the proposed control method to a four-limbed robot traveling across the modelled terrain. The experimental results confirmed that a robot can successfully traverse rough terrain using the proposed crawling motion and that the foot trajectory modification control method can enhance the performance of the robot during such motion.