Herein disclosed is a robot arm mechanism comprising a first arm link mechanism
and a second arm link mechanism, a robot arm driving mechanism for driving the
first arm link mechanism and the second arm link mechanism, and a link retaining
mechanism for pivotably retaining the first arm link mechanism and the second arm
link mechanism, in which a third arm link and a fourth arm link of the first arm
link mechanism are kept forward in a first rotation direction, in which the first
arm link mechanism and the second arm link mechanism are extended, thereby enabling
to prevent the quadric crank chain constituting the robot arm mechanism from being
flattened out while the first arm link mechanism and the second arm link mechanism
are extended, and improving resistance to deformation, in comparison with the conventional
robot arm mechanism.