PURPOSE: To use a motor having a low output power for a drive shaft by providing such an arrangement that the rotation of a first articulatory part between a first member and a second member and the rotation of a second articulatory part between the second member and a third member are made by the unitary rotation of two opposed drive shafts in the first member or the relative rotation therebetween.

CONSTITUTION: In the first articulatory part, when opposed drive shafts 4, 5 are rotated at an equal speed and in the same angular direction (opposite direction as viewed in one direction), gears 7, 8 fixed respectively thereto are rotated in the same direction (opposite directions as viewed in one direction), and accordingly, a gear 9 fixed to one end of a first rotary shaft 10 within a second member 2, or the first rotary shaft 10 is rotated in accordance with a gear ratio, and further a gear 12 fixed to the other end of the first rotary shaft 10 is rotated. Accordingly, a gear 13 fixed to a second rotary shaft 11 or the second rotary shaft 11 is rotated around a second horizontal axis J3, and accordingly, a second arm 14 is turned or tilted around the second horizontal axis J3 by an rotating angle of the opposed drive shafts.