Provided is a robot arm mechanism having high safety reliability. In a robot arm mechanism according to the present invention, a column part (2) having a swiveling rotary joint part (J1) is supportedon a base (1), a hoisting part (4) having a hoisting rotary joint part (J2) is disposed on the column part (2), a linear extension/contraction mechanism (J3) having an arm (5) that can be linearly extended and contracted is provided on the hoisting part (4), and a wrist part (6) to which an end effector can be attached is provided at the distal end of the arm. The wrist part (6) is combined with apan-rotation joint part (J4) for pan-rotating the end effector, a tilt-rotation joint part (J5) for tilt-rotating the end effector forward and backward, and an axial- rotation joint part (J6) for axially rotating the end effector. At least two of J1 to J6 are each provided with a mechanical stopper mechanism that restricts the operation to a mechanical operation range and a safety stopper mechanism that restricts the operation to a safe operable range that is narrower than the mechanical operation range.