Provided is a joint mechanism including two spur gears (9) and (10) a support member (11) that supports the two spur gears (9) and (10) so as to be rotatable about two joint shafts (A) and (B) that are disposed in a skew-lines positional relationship with a space between each other and a rotational-force transmitting mechanism (12) that transmits a rotational force between the spur gears (9) and (10), wherein the rotational-force transmitting mechanism (12) is provided with a transmission member (13) 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 (C) and (D) that are respectively orthogonal to the two joint shafts (A) and (B) and cam mechanisms (14) or linkage mechanisms that are disposed between the transmission member (13) and the two spur gears (9) and (10), respectively, and that convert rotational motions of the spur gears (9) and (10) to a linear motion of the transmission member (13).
