Robot arm mechanism

A robot arm mechanism comprising a linear extension and retraction joint, wherein

• the linear extension and retraction joint includes an arm section, and an ejection section for supporting the arm section,
• the arm section includes a first connection piece string and a second connection piece string,
• the first connection piece string includes a plurality of first connection pieces each having a U-shaped cross section or a hollow square cross section, the second connection piece string includes a plurality of second connection pieces each having a substantially flat plate shape, and the second connection piece string is joined to the first connection piece string to thereby constitute a columnar body having a certain rigidity, and
• the ejection section includes first rollers and second rollers for joining the first and second connection piece strings and supporting the columnar body by joining of the first and second connection piece strings, and the first rollers and the second rollers are disposed with the columnar body sandwiched between the first rollers and the second rollers.