A rigidity of a robot arm mechanism including a linear extension and retraction joint is enhanced. In a robot arm mechanism including the linear extension and retraction joint, the linear extension and retraction joint includes an arm section and an ejection section, the arm section includes a first connection piece string including a plurality of first connection pieces and a second connection piece string including a plurality of second connection pieces, and the second connection piece string is joined to the first connection piece string to thereby constitute a columnar body having a certain rigidity. The ejection section includes lower rollers and upper rollers for joining the first and second connection piece strings and supporting the columnar body. The lower rollers and the upper rollers are disposed with the columnar body sandwiched between the lower rollers and the upper rollers.
