PROBLEM TO BE SOLVED: To provide a reduction gear which further smoothly operates.SOLUTION: A reduction gear 20 comprises an inner tooth gear 15 and an outer tooth gear 16 which are different in the number of teeth, and a cam mechanism 18 which makes the inner tooth gear 15 and the outer tooth gear 16 engaged with each other in an eccentric state. The reduction gear 20 also comprises a connecting shaft 41 which is arranged coaxially with the inner tooth gear 15 by being connected to the cam mechanism 18, and a wheel 52 which can input drive torque for moving an engagement position between the inner tooth gear 15 and the outer tooth gear 16 to the cam mechanism 18 via the connecting shaft 41. The wheel 52 has a long hole 57 extending in a radial direction while passing through a rotation center N3 which is arranged on the same axis of a center position N2 of the outer tooth gear 16, and is connected to the connecting shaft 41 in an eccentric position P equivalent to an eccentric amount δ between the inner tooth gear 15 and the outer tooth gear 16 by the insertion of the connecting shaft 41 into the long hole 57. Then, a long diameter D2 permitting relative movement between the wheel 52 and the connecting shaft 41 along a longitudinal direction of the long hole 57 is set in the long hole 57.

【課題】より円滑に動作する減速装置を提供すること。【解決手段】減速装置２０は、異なる歯数を有した内歯歯車１５及び外歯歯車１６と、内歯歯車１５及び外歯歯車１６を偏心状態で噛合させるカム機構１８とを備える。また、減速装置２０は、カム機構１８に連結されることにより内歯歯車１５と同軸に配置される連結軸４１と、連結軸４１を介して内歯歯車１５及び外歯歯車１６の噛合位置を移動させる駆動トルクをカム機構１８に入力可能なホイール５２とを備える。ホイール５２は、外歯歯車１６の中心位置Ｎ２と同軸上に配置される回転中心Ｎ３を通って径方向に延びる長孔５７を有し、当該長孔５７内に連結軸４１が挿入されることにより、内歯歯車１５と外歯歯車１６との間の偏心量δに相当する偏心位置Ｐにおいて連結軸４１に連結される。そして、この長孔５７には、その長手方向に沿ったホイール５２と連結軸４１との相対移動を許容する長径Ｄ２が設定される。【選択図】図４