Herein disclosed is a robot arm mechanism comprising: a first handling member for supporting and handling a first object; a second handling member for supporting and handling a second object; a first robot arm including a first arm link and a second arm link, the first end portion of the second arm link being pivotably connected to the second end portion of the first arm link, and the second end portion of the second arm link being connected to the first handling member to allow the first handling member to support the first object in a stable condition; a second robot arm including a first arm link and a second arm link, the first end portion of the second arm link being pivotably connected to the second end portion of the first arm link, the second arm link being inclined with respect to the second arm link of the first robot arm at a preset angle defined between the central line of the second arm link of the second robot arm and the central line of the second arm link of the first robot arm, and the second end portion of the second arm link being connected to the second handling member to allow the second handling member to support the second object in a stable condition; a robot arm moving mechanism for allowing one of the first arm links and of the first and second robot arms to be angularly moved with respect to the other of the first arm links of the first and second robot arms; and an angle keeping mechanism for keeping substantially fixed the preset angle defined between the central line of the second arm link of the second robot arm and the central line of the second arm link of the first robot arm as one of the first arm links of the first and second robot arms is angularly moved with respect to the other of the first arm links of the first and second robot arms.