Linear expansion/contraction mechanism

A purpose of the present invention is to reduce the cost of a linear expansion/contraction mechanism. This linear expansion/contraction mechanism that is equipped to a robot arm mechanism comprises: a plurality of plate-shaped first segments (53) that are bendably connected to one another at front and back end surfaces thereof; a plurality of groove-shaped second segments (54) that are bendably connected to one another at front and back end surfaces of bottom parts thereof; a linking part that becomes rigid in a linear shape when the first and second segments (53, 54) are joined to one another, returns to a bending condition when the first and second segments (53, 54) are separated from one another, and links the forwardmost of the plurality of first segments (53) and the forwardmost of the plurality of second segments (54); and an advancing mechanism part that is equipped with a plurality of rollers (59, 60) in order to strongly join the first and second segments (53, 54) and to provide support such that the same can freely move forward and back, wherein at least one groove part (551-554) is formed, along a forward/backward direction, in each surface of the first and second segments (53, 54) that comes into contact with the rollers (59, 60).