A rotational driving mechanism for driving a first member and a second member, which are part of a robot, to rotate relatively on a predetermined rotational driving plane by means of a linear motion actuator having a linear motion output shaft, includes: a first link unit with which the output shaft is connected, and which is arranged so as to be rotatable with respect to the first member through a first rotation shaft, and which is also arranged so as to be rotatable with respect to the second member side through a second rotation shaft; a second link unit which is connected with a first support shaft arranged at the first member side, and which is connected with a second support shaft arranged at the second member side, with a center distance between the first support shaft and the second support shaft being made constant.