PURPOSE: To widen the operation range of a robot arm by connecting second links on different levels between each first link and each third link of two pairs of parallel link mechanisms arranged in parallel with each other.

CONSTITUTION: Power of a motor 4 is transmitted to a double-shaft arm 10 provided in a load side through a parallel link mechanism formed of first links 5a, 5b, second links 6a, 6b and third links 7a, 7b. At this stage, two pairs of parallel link mechanisms (5a, 6a, 7a), (5b, 6b, 7b) are arranged in parallel with each other, and second links 6a, 6b of each pair are connected on different levels between the first links 5a, 5b and the third links 7a, 7b. As a result, in a singular point, in which one of parallel link mechanism (for example, 5a, 6a, 7a) are arranged on a straight line so as to be overlapped with each other, the double-shaft arm 10 is driven by other parallel link mechanism (5b, 6b, 7b). With this structure, operation range of the double-shaft arm 10 is widened.