A compliant joint capable of achieving passive compliance for a robot in order to prevent an injury to a human by collision with the robot. The compliant joint includes a housing, a cam member rotatably mounted in the housing, a roller spring device mounted to the cam member to be compressed and extended, a guiding member formed in the housing to guide compression and extension of the roller spring device in accordance with rotation of the cam member, and a receiving recess formed at the guiding member to engage the housing and the cam member with each other by receiving the roller spring device and release the engagement by separating from the roller spring device. Accordingly, robustness of the robot can be maintained when an impact less than a predetermined magnitude is applied, while being suddenly decreased when an impact greater than the magnitude is applied.