Provided is a joint mechanism including two spur gears and a support member that supports the two spur gears and so as to be rotatable about two joint shafts and that are disposed in a skew-lines positional relationship with a space between each other and a rotational-force transmitting mechanism that transmits a rotational force between the spur gears and, wherein the rotational-force transmitting mechanism is provided with a transmission member formed of a rigid piece that is supported so as to be movable only in a direction parallel to a line of intersection between planes and that are respectively orthogonal to the two joint shafts and cam mechanisms or linkage mechanisms that are disposed between the transmission member and the two spur gears and, respectively, and that convert rotational motions of the spur gears and to a linear motion of the transmission member.
