A workpiece holding mechanism having a first arm and a second arm configured to be movable in a three-dimensional space, comprising: a first support provided to a tip of the first arm and having a first surface part defined by one of a surface extending in a first direction in a horizontal plane and a plurality of surfaces aligned in the first direction; a second support provided to a tip of the second arm, and having a second surface part opposed to the first surface part and defined by one of a surface extending in the first direction and by a plurality of surfaces aligned in the first direction; a third support provided to the first support, and having a third surface part located closer to the second surface part than the first surface part is and located at a height corresponding to a lower end of the first surface part; a fourth support provided to the second support, and having a fourth surface part located closer to the first surface part than the second surface part is and located at a height corresponding to a lower end of the second surface part; a fifth support provided to the first support, and having a fifth surface part located, at one end of the first surface part in the first direction, closer to the second surface part than the first surface part is and located above the third surface part; and a sixth support provided to the second support, and having a sixth surface part is located, at an end portion of the second surface part opposed to the one end of the first surface part in the first direction, closer to the first surface part than the second surface part is and located above the fourth surface part, wherein the fifth support is arranged at a base end portion side of the first support, and the sixth support is arranged at a tip portion side of the second support, wherein at least one of the third surface part and the fourth surface part is defined by one of a surface extending in the first direction and a plurality of surfaces aligned in the first direction. a first support provided to a tip of the first arm and having a first surface part defined by one of a surface extending in a first direction in a horizontal plane and a plurality of surfaces aligned in the first direction; a second support provided to a tip of the second arm, and having a second surface part opposed to the first surface part and defined by one of a surface extending in the first direction and by a plurality of surfaces aligned in the first direction; a third support provided to the first support, and having a third surface part located closer to the second surface part than the first surface part is and located at a height corresponding to a lower end of the first surface part; a fourth support provided to the second support, and having a fourth surface part located closer to the first surface part than the second surface part is and located at a height corresponding to a lower end of the second surface part; a fifth support provided to the first support, and having a fifth surface part located, at one end of the first surface part in the first direction, closer to the second surface part than the first surface part is and located above the third surface part; and a sixth support provided to the second support, and having a sixth surface part is located, at an end portion of the second surface part opposed to the one end of the first surface part in the first direction, closer to the first surface part than the second surface part is and located above the fourth surface part, wherein the fifth support is arranged at a base end portion side of the first support, and the sixth support is arranged at a tip portion side of the second support, wherein at least one of the third surface part and the fourth surface part is defined by one of a surface extending in the first direction and a plurality of surfaces aligned in the first direction.